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starry sky above a brick chapel
The night sky above a French chapel with the Milky Way and stars visible, and light pollution on the horizon

Night, or nighttime, is the period of darkness when the Sun is below the horizon. Daylight illuminates one side of the Earth, leaving the other in darkness. The opposite of nighttime is daytime. Earth's rotation causes the appearance of sunrise and sunset. Moonlight, airglow, starlight, and light pollution dimly illuminate night. The duration of day, night, and twilight varies depending on the time of year and the latitude. Night on other celestial bodies is affected by their rotation and orbital periods. The planets Mercury and Venus have much longer nights than Earth. On Venus, night lasts about 58 Earth days. The Moon's rotation is tidally locked, rotating so that one of the sides of the Moon always faces Earth. Nightfall across portions of the near side of the Moon results in lunar phases visible from Earth.

Organisms respond to the changes brought by nightfall: darkness, increased humidity, and lower temperatures. Their responses include direct reactions and adjustments to circadian rhythms governed by an internal biological clock. These circadian rhythms, regulated by exposure to light and darkness, affect an organism's behavior and physiology. Animals more active at night are called nocturnal and have adaptations for low light, including different forms of night vision and the heightening of other senses. Diurnal animals are active during the day and sleep at night; mammals, birds, and some others dream while asleep. Fungi respond directly to nightfall and increase their biomass. With some exceptions, fungi do not rely on a biological clock. Plants store energy produced through photosynthesis as starch granules to consume at night. Algae engage in a similar process, and cyanobacteria transition from photosynthesis to nitrogen fixation after sunset. In arid environments like deserts, plants evolved to be more active at night, with many gathering carbon dioxide overnight for daytime photosynthesis. Night-blooming cacti rely on nocturnal pollinators such as bats and moths for reproduction. Light pollution disrupts the patterns in ecosystems and is especially harmful to night-flying insects.

Historically, night has been a time of increased danger and insecurity. Many daytime social controls dissipated after sunset. Theft, fights, murders, taboo sexual activities, and accidental deaths all became more frequent due in part to reduced visibility. Despite a reduction in urban dangers, the majority of violent crime is still committed after dark. According to psychologists, the widespread fear of the dark and the night stems from these dangers. The fear remains common to the present day, especially among children.

Cultures have personified night through deities associated with some or all of these aspects of nighttime. The folklore of many cultures contains "creatures of the night", including werewolves, witches, ghosts, and goblins, reflecting societal fears and anxieties. The introduction of artificial lighting extended daytime activities. Major European cities hung lanterns housing candles and oil lamps in the 1600s. Nineteenth-century gas and electric lights created unprecedented illumination. The range of socially acceptable leisure activities expanded, and various industries introduced a night shift. Nightlife, encompassing bars, nightclubs, and cultural venues, has become a significant part of urban culture, contributing to social and political movements.

Etymology

[edit]
manuscript lines
Variable spellings of night in a Middle English poem:
  • Þu sittest a dai & fliȝst a niȝt (top)
  • Þu sittest a day and flyhst a niht (bottom)
  • 'You sit by day and fly by night'

The word night is derived from the Old English niht. Both words are Germanic and cognates of the German nacht.[1] The terms belong to a family of night words present in nearly all European languages, derived from an Indo-European word, reconstructed as *nekwt.[2][3] The original root is thought most likely to be *nek-, a term relating to death.[3] According to the nineteenth-century British philologist Walter William Skeat, this root meant 'to perish', 'to disappear', or 'to fail', with night being the point where light ceased and perished.[4] More recently, Roland Pooth has argued for the root term to be understood to mean 'empty' or 'naked', with night being the point where the sky is naked and empty of light.[5] As a result of this early origin, night shares its root with the Latin nox,[1] the root of many English terms connected to the night, such as equinox and nocturnal.[6][2]

Cognates of day are less widespread. Philologist Ernest Weekley attributed the many related night words to the early practice of measuring time in nights rather than days.[7] The term fortnight, an Old English contraction of "fourteen nights", is a remnant of this ancient custom of measuring time in nights.[6]

The letters "gh" were added to the word to represent the yogh character (Ȝ), unavailable on printing presses imported from continental Europe in the fifteenth and sixteenth centuries. As English speakers ceased to pronounce the yogh, the "gh" became silent. A similar process occurred in many English words, such as light.[8]

Astronomy

[edit]

A planet's rotation causes nighttime and daytime. When a place on Earth is pointed away from the Sun, that location experiences night. The Sun appears to set in the West and rise in the East due to Earth's rotation.[9] Many celestial bodies, including the other planets in the solar system, have a form of night.[9][10]

Earth

[edit]
diagram, explained in section
Day and night during the winter solstice in the northern hemisphere

The length of night on Earth varies depending on the time of year. Longer nights occur in winter, with the winter solstice being the longest.[11] Nights are shorter in the summer, with the summer solstice being the shortest.[11] Earth orbits the Sun on an axis tilted 23.44 degrees.[12] Nights are longer when a hemisphere is tilted away from the Sun and shorter when a hemisphere is tilted toward the Sun.[13] As a result, the longest night of the year for the Northern Hemisphere will be the shortest night of the year for the Southern Hemisphere.[13]

Night's duration varies least near the equator. The difference between the shortest and longest night increases approaching the poles.[14] At the equator, night lasts roughly 12 hours throughout the year.[15] The tropics have little difference in the length of day and night.[14] At the 45th parallel, the longest winter night is roughly twice as long as the shortest summer night.[16] Within the polar circles, night will last the full 24 hours of the winter solstice.[13] The length of this polar night increases closer to the poles. Utqiagvik, Alaska, the northernmost point in the United States, experiences 65 days of polar night.[17] At the pole itself, polar night lasts 179 days from September to March.[17]

diagram; follow link for details
Diagram of atmospheric refraction at sunrise and sunset

Over a year, there is more daytime than nighttime because of the Sun's size and atmospheric refraction. The Sun is not a single point.[18] Viewed from Earth, the Sun ranges in angular diameter from 31 to 33 arcminutes.[19] When the center of the Sun falls to the western horizon, half of the Sun will still be visible during sunset. Likewise, by the time the center of the Sun rises to the eastern horizon, half of the Sun will already be visible during sunrise.[20] This shortens night by about three minutes in temperate zones.[21] Atmospheric refraction is a larger factor.[18] Refraction bends sunlight over the horizon.[21] On Earth, the Sun remains briefly visible after it has geometrically fallen below the horizon.[21] This shortens night by about six minutes.[21] Scattered, diffuse sunlight remains in the sky after sunset and into twilight.[22]

space photograph showing the inhabited areas of the Nile glowing against the dark desert
The drainage basin of the Nile River and delta at night

Twilight, the gradual transition to and from darkness when the Sun is below the horizon, has multiple stages.[23] "Civil" twilight occurs when the Sun is between 0° and 6° below the horizon. Nearby planets like Venus and bright stars like Sirius are visible during this period.[24] "Nautical" twilight continues until the Sun is 12° below the horizon.[25] During nautical twilight, the horizon is visible enough for navigation.[26] "Astronomical" twilight continues until the Sun has sunk 18° below the horizon.[24][27] Beyond 18°, refracted sunlight is no longer visible.[27] The period when the sun is 18° or more below either horizon is called astronomical night.[25]

Similar to the duration of night itself, the duration of twilight varies according to latitude.[27] At the equator, day quickly transitions to night, while the transition can take weeks near the poles.[27] The duration of twilight is longest at the summer solstice and shortest near the equinoxes.[28] Moonlight, starlight, airglow, and light pollution can dimly illuminate the nighttime, with their diffuse aspects being termed skyglow.[29][30] The amount of skyglow increases each year due to artificial lighting.[29]

Other celestial bodies

[edit]
The Moon's phases at hourly intervals throughout 2020, as viewed from the Northern Hemisphere

Night exists on the other planets and moons in the Solar System.[9][10] The length of night is affected by the rotation period and orbital period of the celestial object.[31] The lunar phases visible from Earth result from nightfall on the Moon.[32] The Moon has longer nights than Earth, lasting about two weeks.[31] This is half of the synodic lunar month, the time it takes the Moon to cycle through its phases.[33] The Moon is tidally locked to Earth; it rotates so that one side of the Moon always faces the Earth.[34] The side of the Moon facing away from Earth is called the far side of the Moon, and the side facing Earth is called the near side of the Moon. During lunar night on the near side, Earth appears 50 times brighter than a full moon appears from Earth.[35] Because the Moon has no atmosphere, there is an abrupt transition from day to night without twilight.[36]

photograph of hazy and distant sunset
Sunset on Mars

Night varies from planet to planet within the Solar System. Mars's dusty atmosphere causes a lengthy twilight period. The refracted light ranges from purple to blue, often resulting in glowing noctilucent clouds.[37] Venus and Mercury have long nights because of their slow rotational periods.[38] The planet Venus rotates once every 243 Earth days.[39] Because of its unusual retrograde rotation, nights last just over 58 Earth days.[40] The dense greenhouse atmosphere on Venus keeps its surface hot enough to melt lead throughout the night.[41][42] Its planetary wind system, driven by solar heat, reverses direction from day to night. Venus's winds flow from the equator to the poles on the day side and from the poles to the equator on the night side.[43][44] On Mercury, the planet closest to the Sun, the temperature drops by over 1,000 °F (538 °C) after nightfall.[45]

The day–night cycle is one consideration for planetary habitability or the possibility of extraterrestrial life on distant exoplanets.[46] In general, shorter nights result in a higher equilibrium temperature for the planet.[47] On an Earth-like planet, longer day–night cycles may increase habitability up to a point.[48] Computer models show that longer nights would affect Hadley circulation, resulting in a cooler, less cloudy planet.[49] Once the rotation speed of a planet slows beyond 1/16 that of Earth, the difference in day-to-night temperature shifts increases dramatically.[48] Some exoplanets, like those of TRAPPIST-1, are tidally locked. Tidally locked planets have equal rotation and orbital periods, so one side experiences constant day, and the other side constant night. In these situations, astrophysicists believe that life would most likely develop in the twilight zone between the day and night hemispheres.[50][51]

Biology

[edit]
The giant moray eel is most active by night. Its brain has adapted to rely less on visual input and more on its sense of smell.[52]

Living organisms react directly to the darkness of night.[53] Light and darkness also affect circadian rhythms, the physical and mental changes that occur in a 24-hour cycle.[54] This daily cycle is regulated by an internal "biological clock" that is adjusted by exposure to light.[54] The length and timing of nighttime depend on location and time of year.[55] Organisms that are more active at night possess adaptations to the night's dimmer light, increased humidity, and lower temperatures.[56]

Animals

[edit]

Animals that are active primarily at night are called nocturnal and usually possess adaptations for night vision.[57] In vertebrates' eyes, two types of photoreceptor cells sense light.[58] Cone cells sense color but are ineffective in low light; rod cells sense only brightness but remain effective in very dim light.[59] The eyes of nocturnal animals have a greater percentage of rod cells.[58] In most mammals, rod cells contain densely packed DNA near the edge of the nucleus. For nocturnal mammals, this is reversed with the densely packed DNA in the center of the nucleus, which reduces the scattering of light.[60] Some nocturnal animals have a mirror, the tapetum lucidum, behind the retina. This doubles the amount of light their eyes can process.[61]

Many insects fly towards a work light.
Nocturnal insects drawn to an artificial light

The compound eyes of insects can see at even lower levels of light. For example, the elephant hawk moth can see in color, including ultraviolet, with only starlight.[57] Nocturnal insects navigate using moonlight, lunar phases, infrared vision, the position of the stars, and the Earth's magnetic field.[62] Artificial lighting disrupts the biorhythms of many animals.[63] Night-flying insects that use the moon for navigation are especially vulnerable to disorientation from increasing levels of artificial lighting.[64] Artificial lights attract many night-flying insects that die from exhaustion and nocturnal predators.[65] Decreases in insect populations disrupt the overall ecosystem because their larvae are a key food source for smaller fish.[66] Dark-sky advocate Paul Bogard described the unnatural migration of night-flying insects from the unlit Nevada desert into Las Vegas as "like sparkling confetti floating in the beam's white column".[67]

Time-expanded recording of a bat using echolocation to home in on its prey

Some nocturnal animals have developed other senses to compensate for limited light. Many snakes have a pit organ that senses infrared light and enables them to detect heat. Nocturnal mice possess a vomeronasal organ that enhances their sense of smell. Bats heavily depend on echolocation.[68] Echolocation allows an animal to navigate with their sense of hearing by emitting sounds and listening for the time it takes them to bounce back.[68] Bats emit a steady stream of clicks while hunting insects and home in on prey as thin as human hair.[69]

painting of a demon on the chest of a sleeping woman
Fuseli's The Nightmare

People and other diurnal animals sleep primarily at night.[70] Humans, other mammals, and birds experience multiple stages of sleep visible via electroencephalography.[71] The stages of sleep are wakefulness, three stages of non-rapid eye movement sleep (NREM), including deep sleep, and rapid eye movement (REM) sleep.[72] During REM sleep, dreams are more frequent and complex.[73] Studies show that some reptiles may also experience REM sleep.[74] During deep sleep, memories are consolidated into long-term memory.[75] Invertebrates most likely experience a form of sleep as well. Studies on bees, which have complex brain structures unrelated to vertebrate brains, have shown improvements in memory after sleep, similar to mammals.[76]

Compared to waking life, dreams are sparse with limited sensory detail. Dreams are hallucinatory or bizarre, and they often have a narrative structure.[77] Many hypotheses exist to explain the function of dreams without a definitive answer.[77] Nightmares are dreams that cause distress. The word "night-mare" originally referred to nocturnal demons that were believed to assail sleeping dreamers, like the incubus (male) or succubus (female).[78] It was believed that the demons could sit upon a dreamer's chest to suffocate a victim, as depicted in John Henry Fuseli's The Nightmare.[78]

Fungi

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Tendrils protrude through the corpse of a dead insect host still clinging to a plant.
An entomopathogenic fungus extends fruiting bodies from its host.

Fungi can sense the presence and absence of light, and the nightly changes of most fungi growth and biological processes are direct responses to either darkness or falling temperatures.[55] By night, fungi are more engaged in synthesizing cellular components and increasing their biomass.[79] For example, fungi that prey on insects will infect the central nervous system of their prey, allowing the fungi to control the actions of the dying insect. During the late afternoon, the fungi will pilot their prey to higher elevations where wind currents can carry its spores further, and at night, will kill and digest the insect, extending fruiting bodies from the host's exoskeleton.[80] Most fungi do not have true circadian rhythms.[55] The bread mold Neurospora crassa is used to study biorhythms because it is one of the few species of fungi to rely on an internal clock rather than directly on environmental changes.[81]

Plants

[edit]
Time-lapse video of a night-blooming cereus

During the day, plants engage in photosynthesis and release oxygen. By night, plants engage in respiration, consuming oxygen and releasing carbon dioxide.[82] Plants can draw up more water after sunset, which facilitates new leaf growth.[83] As plants cannot create energy through photosynthesis after sunset, they use energy stored in the plant, typically as starch granules.[84] Plants use this stored energy at a steady rate, depleting their reserves almost right at dawn.[84] Plants will adjust their rate of consumption to match the expected time until sunrise. This avoids prematurely running out of starch reserves,[84] and it allows the plant to adjust for longer nights in the winter.[85] If a plant is subjected to artificially early darkness, it will ration its energy consumption to last until dawn.[85]

Succulent plants, including cacti, have adapted to the limited water availability in arid environments like deserts.[86] The stomata of cacti do not open until night.[87] When the temperature drops, the pores open to allow the cacti to store carbon dioxide for photosynthesis the next day, a process known as crassulacean acid metabolism (CAM).[87][88] Cacti and night-blooming plants use CAM to store up to 99% of the carbon dioxide they use in daily photosynthesis.[89][90] Ceroid cacti often have flowers that bloom at night and fade before sunrise.[91] As few bees are nocturnal, night-flowering plants rely on other pollinators, including moths, beetles, and bats.[92] These flowers rely more on the pollinators' sense of smell, with strong perfumes to attract moths and foul-smelling odors to attract bats.[93]

Eukaryotic and prokaryotic organisms that engage in photosynthesis are also affected by nightfall. Like plants, algae will switch to taking in oxygen and processing energy stored as starch.[94][95] Cyanobacteria switch from photosynthesis to nitrogen fixation after sunset.[96] They also absorb genetic material from their environment at a higher rate during the night.[97]

Culture

[edit]

History and technology

[edit]
a lantern illuminates only the corner of the room where it is pointed
An illustration from Horatio Alger's Tom Temple's Career shows a burglar using a "dark lantern", which shines in only one direction.

Before the industrial era, night was a time of heightened insecurity.[98] Fear of the night was common but varied in intensity across cultures.[99] Some psychologists have concluded that prehistoric people feared real and tangible harms present during the night and that these concrete fears developed into a broader fear of night itself.[100]

Dangers increased due to lower visibility. Injuries and deaths were caused by drowning and falling into pits, ditches, and shafts.[101] People were less able to evaluate others after dark.[102] Due to nocturnal alcohol consumption and the anonymity of darkness, quarrels were more likely to escalate to violence. For example, in medieval Stockholm, the majority of murders were committed while intoxicated.[103]

Crime and fear of crime increased at night.[104] In pre-industrial Europe, criminals disguised themselves with hats, face paint, or cloaks. Thieves would trip pedestrians with ropes laid across streets and dismount horse riders using long poles extended from the roadside shadows. They used "dark lanterns" where light could be shined through a single side. Most nocturnal thieves worked alone; organized criminal gangs were uncommon except for burglary.[105] With members numbering into the dozens and hundreds, burglary rings hacked, cut, smashed, and burrowed into homes when residents were sleeping. They used a range of brutality to subdue and intimidate the residents, with the French chauffeurs infamously torturing victims with fire. With nothing comparable to a modern police force, these burglary gangs then escaped into the night, often disguised as demons, ghosts, or monsters.[106] Burglary rings also employed arson both to create distraction and to flush people from their locked homes.[107]

Early sources of heat and illumination (such as chimneys, candles, and oil lamps) created inherent fire risks while families slept.[108] Additionally, bakers and brewers kept fires constantly burning near stacks of wood and charcoal.[109] Cities and towns regularly burned to the ground. One English town, Stratford-upon-Avon, was consumed by fire four times in five years.[110] The increased humidity of night was deemed the result of vapors and fumes.[111] The annual movements of stars and constellations across the night sky were used to track the passage of time,[112] but other changes in the night sky were interpreted as significant omens.[113]

Many daytime religious, governmental, and local social controls dissipated after nightfall.[114] Fortified Christian communities announced the coming darkness with horns, church bells, or drums. This alerted residents—like peasants working in the fields—to return home before the city gates shut.[115] The English engaged in a daily process of "shutting in", where valuables were brought into homes before they were bolted, barred, locked, and shuttered.[116] Many English and European towns attempted to impose curfews during the medieval period and gradually loosened the restrictions via exceptions.[117] Prayer and folk magic were more common by night.[118] Amulets were hung to ward off nightmares, spells were cast against thievery, and pig hearts were hung in chimneys to block demons from traveling down them.[119] The common phrase "good night" has been shortened from "God give you a good night."[118] In Ottoman Istanbul, the royal palaces shifted to projecting nocturnal power through large parties lit by lanterns, candles, and fireworks.[120] Though alcohol was forbidden for Muslims, after dark, Turkish Muslims went to bars and taverns beyond the Muslim areas.[121]

The night has long been a time of increased sexual activity, especially in taboo forms such as premarital, extramarital, gay, and lesbian sex.[122] In colonial New England courtship, young unmarried couples practiced bundling before marriage. The couples would lie down in the woman's bed, her family would wrap them tightly with blankets, and they would spend the night together this way. Some families took precautions to prevent unintended pregnancies, like sleeping in the same room, laying a large wooden board between the couple, or pulling a single stocking over both of their daughter's legs.[123] Historian Roger Ekirch described pre-industrial night as a "sanctuary from ordinary existence."[124]

A lamplighter lights the lantern within a lowered light fixture mounted on the side of a building.
Lantern
A lamplighter climbs a ladder to light a gas streetlight.
Gas
The first streetlights in Europe were suspended lanterns that housed candles or lamps. Much brighter gas lighting was developed in the 1800s.[125]

Artificial lighting expanded the scope of acceptable work and leisure after dark.[126] In the 1600s, the major European cities introduced streetlights. These were lit by lamplighters each evening outside of the summer months.[127] Early streetlights were metal and glass enclosures housing candles or oil lamps. They were suspended above streets or mounted on posts.[128] The use of artificial lighting led to an increase in acceptable nightlife.[129] In more rural areas, night remained a period of rest and nocturnal labor.[130] Young adults, the urban poor, prostitutes, and thieves benefited from the anonymity of darkness and frequently smashed the new lanterns.[131] Gas lighting was invented in the 1800s. A gas mantle was over ten times brighter than an oil lamp.[132] Gas lighting was associated with the creation of regular police forces.[133] In England, police departments were tasked with maintaining the gas lights, which became known as "police lamps".[134] Daytime routines were further pushed back into the night by the electric light bulb—invented in the late 19th century—and the widespread usage of newer timekeeping devices like watches.[135] Electric lights created night shifts for traditionally daytime fields, like India's cotton industry, and created opportunities for working adults to attend night school.[136]

Fear of the dark

[edit]

The widespread usage of artificial lighting and other technologies has allowed many aspects of daily life and daytime social controls to continue after sunset. Fear of the dark and belief in creatures of the night has decreased but remains a significant part of modern life. One side effect of measures to police and promote urban nightlife is reduced personal privacy. Another side effect is the emergence of 8-hour sleep cycles replacing segmented sleep.[137] Before the widespread usage of artificial lighting, sleep was typically split into two major segments separated by about an hour of wakefulness.[138] During this midnight period, people engaged in prayer, crimes, urination, sex, and, most commonly, reflection.[139] Without exposure to artificial light, studies show that people revert to sleeping in two separate intervals.[140]

Fear of the dark and the night remains widespread and only amounts to a phobia in rare cases.[141] Nighttime fears are especially common among children.[142] These fears are typically mild, and most children grow out of them. About 1 in 5 children have persistent and intense fears that correlate with decreased sleep quality and anxiety for both the child and their family.[143] Lucretius and Aristotle observed a similar fear of the dark more present among children in the classical era,[144] and there are long traditions among various cultures of telling children bedtime stories of bogeymen and villains who prey upon disobedient children.[145]

Among adults, walking alone after dark is a common nighttime fear. It is so common, that criminologists have used some variation of the question, "How safe do you feel or would you feel being alone in your neighbourhood after dark?" to gauge a population's fear of crime and victimization.[146] The fear is most strongly reported by women and sexual minorities.[147] A 1975 study found that the most common nighttime fears expressed by women were murder and sexual assault.[148] Despite most urban crimes correlating to daytime hours of peak activity, violent crime remains most common after dark.[149]

Folklore and religion

[edit]
mask made from human skull
Mask of Tezcatlipoca, the Aztec "Night Wind"

Diverse cultures have made connections between the night sky and the afterlife.[150] Many Native American peoples have described the Milky Way as a path where the deceased travel as stars. The Lakota term for the Milky Way is Wanáǧi Thacháŋku, or "Spirit's Road".[151] In Mayan mythology, the Milky Way's dark band is the Road of Xibalba, the path to the underworld.[151] Unrelated cultures share a myth of a star-covered sky goddess who arches over the planet after sunset, like Citlālicue, the Aztec personification of the Milky Way.[152][153] The elongated Egyptian goddess Nut and N!adima from Botswana are said to consume the Sun at dusk.[154] In the Ancient Egyptian religion, the Sun then travels through the netherworld inside Nut's body, where it is reborn at dawn.[154]

painting
Nótt, the personification of night in Norse mythology, rides her horse in this 1887 painting by Peter Nicolai Arbo.

Many cultures have personified the night.[100] Ratri is the star-covered Hindu goddess of the night.[155] In the Icelandic Prose Edda, night is embodied by Nótt.[156] Ratri and Nött are goddesses of sleep and rest, but it is common for personifications to be associated with misfortune.[100] In Aztec mythology, Black Tezcatlipoca, the "Night Wind", was associated with obsidian and the nocturnal jaguar.[157][158] In his "Precious Owl" manifestation, the Aztecs regarded Tezcatlipoca as the bringer of death and destruction.[157] The Aztecs anticipated an unending night when the Tzitzimīmeh, skeletal female star deities, would descend to consume all humans.[159] In classical mythology, the night goddess Nyx is the mother of Sleep, Death, Disease, Strife, and Doom.[160] In Jewish culture and mysticism, the demon Lilith embodies the emotional reactions to darkness, including terror, lust, and liberation.[161]

Nighttime in the pre-industrial period, often called the "night season", was associated with darkness and uncertainty.[162] Various cultures have regarded the night as a time when ghosts and other spirits are active on Earth.[163] When Protestant theologians abandoned the concept of purgatory, many came to view reported ghost sightings as the result of demonic activity.[164] In the sixteenth century, Swiss theologian Ludwig Lavater began attempting to explain reported spirits as mistakes, deceit, or the work of demons.[165] The idea of night as a dangerous, dark, or haunted time persists in modern urban legends like the vanishing hitchhiker.[166][167]

Many times in the night season, there have been certain spirits heard softly going or spitting or groaning, who being asked what they were have made answer that they were the souls of this or that man and that they now endure extreme torments.[168]

— Ludwig Lavater, Of Ghosts and Spirits Walking by Night

In folklore, nocturnal preternatural beings like goblins, fairies, werewolves, pucks, brownies, banshees, and boggarts have overlapping but non-synonymous definitions.[169] The werewolf—and its francophone variations, the loup-garou and rougarou—were believed to be people who transformed into beasts at night.[170][171] In West Africa and among the African diaspora, there is a widespread tradition of a type of vampire who removes their human skin at night and travels as a blood-sucking ball of light. Variation includes the feu-follet, the Surinamese asema, the Caribbean sukuyan, the Ashanti obayifo, and the Ghanaian asanbosam.[172][173] The medieval fear of night-flying European witches was influenced by the Roman strix.[174] The Romans described the strix as capable of changing between a beautiful woman and an owl-shaped monster.[175] Common themes among these mythical nocturnal entities include hypersexuality, predation, shapeshifting, deception, mischief, and malice.[176]

Nightlife

[edit]
Main article: Nightlife
many pedestrians, drivers, and seated people active at night and lit by streetlights, headlights, and billboards
Nightlife in Times Square, Midtown Manhattan

Nightlife, sometimes referred to as "the night-time economy", is a range of entertainment available and generally more popular from the late evening into the early morning.[177][178] It has traditionally included venues such as pubs, bars, nightclubs, live music, concerts, cabarets, theaters, hookah lounges, cinemas, and shows. Nightlife entertainment is often more adult-oriented than daytime entertainment.[179] It also includes informal gatherings like parties, botellón, gymkhanas, bingo, and amateur sports.[177] In many cities, there has been an increasing focus on nightlife catering to tourists.[180] Nightlife has become a major part of the economy and urban planning in modern cities.[181] People who prefer to be active at night are called night owls.[182]

Social movements in the 20th century, including feminism, black activism, the gay rights movement, and community action, blurred the lines between political action and broader cultural activities, making political movements a part of the nightlife.[183] Sociologists have argued that vibrant city nightlife scenes contribute to the development of culture and political movements. David Grazian cites as examples the development of beat poetry, musical styles including bebop, urban blues, and early rock, and the importance of nightlife for the development of the gay rights movement in the United States kicked off by the riots at the Stonewall Inn nightclub in Greenwich Village, Lower Manhattan, New York City.[184] Modern cities treat nightlife as necessary to the city's marketability but also something to be managed in order to reduce activities viewed as disorderly, risky, or otherwise problematic.[185] Urban renewal policies have increased the available possibilities for nighttime consumers and decreased non-commercial nocturnal activities outside of sanctioned festivals and concerts.[186]

Art

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Literature

[edit]
The Sphere by Marcus Manilius, translated into English by Edward Sherburne in the 17th century

In literature, night is often associated with mysterious, hidden, dangerous, and clandestine activities.[187] Rhesus is the only extant Greek tragedy where night is explicitly invoked and made an element of the story. In the play, night is a time of disorder and confusion that allows Odysseus to sneak into the Trojan camp and kill King Rhesus of Thrace.[188] The handful of surviving Classical Greek texts that describe the nocturnal activities of women portray female freedom, especially to speak openly, male anxieties about that freedom, and magic that functions as a metaphor for nocturnal danger.[189] Roman poets like Marcus Manilius and Aratus worked late into the night and incorporated darkness and the night sky into their writing.[190]

Since the Age of Enlightenment, nocturnal settings have been a frequent place for passionate chaos as a counterbalance to the rationality present during the day.[191] In Gothic fiction, this absence of rationality offered a space for lust and terror.[192] Ottoman literature portrayed night as a time for forbidden or unrequited love.[193] Night and day were long depicted as opposite conditions.[194] The electric light, the industrial revolution, and shift work brought many aspects of daily life into the night.[187] The author Charles Dickens lived in London during the time of gas lighting and compared the unstable separation between the waking and sleeping city to the unstable separation he perceived between dream and delusion.[195][196] Night in contemporary literature offers liminal settings, such as hospitals and gas stations, that contain some aspects of daily life.[187]

Night fell, while Helga Crane in the rushing swiftness of a roaring elevated train sat numb. It was as if all the bogies and goblins that had beset her unloved, unloving, and unhappy childhood had come to life with tenfold power to hurt and frighten.[197]

— Nella Larsen, Quicksand

Film and photography

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A night scene tinted blue from the 1925 film The Phantom of the Opera

Directly filming at night is rarely done. Film stocks and video cameras are much less sensitive in low-light environments than the human eye.[198] During the silent film era, many night scenes were filmed during the day in black and white.[199] Sections of the monochrome film reel with exterior night scenes were soaked in an acidic dye that tinted the whole scene blue.[200][201] "Day for night" is a set of cinematic techniques that simulate a night scene while filming in daylight. They include underexposing to soften the scene, using a graduated neutral-density filter to mute lighting, and setting up the artificial lighting to amplify shadows in the background. [202] Lower-budget films are more likely to use day for night shooting; larger-budget films are more likely to film at night with artificial lighting.[202] Cinematographers have used tinting, filters, color balance settings, and physical lights to color night scenes blue.[203] In low light, people experience the Purkinje effect, which causes reds to dim so that more blue is perceived. As light decreases towards total darkness, the human eye has more scotopic vision, relying more on rod cells and being less able to perceive color.[204][199]

A ferris wheel blurs into a neon circle.
A long-exposure photograph of the London Eye at night

Night photography can capture the natural colors of night by increasing the exposure time, or length of time captured in the photography.[205] Longer exposures open the possibility for photographers to use light painting to selectively illuminate a scene.[206] Digital photography can also make use of high-ISO settings, which increase the sensitivity to light, to take shorter exposure shots. This makes it possible to capture moving subjects without turning their movements into a blur.[207]

Painting

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Main articles: Night in paintings (Eastern art) and Night in paintings (Western art)

Dating back to prehistoric cave paintings, artists have used a range of symbols to denote and depict the night sky.[208] The first widely accepted portrayal of the night sky is the Nebra sky disc created c. 1600 BC.[208] In medieval art, astrological signs gave meaning to paintings of night scenes.[208] Adam Elsheimer's paintings on copper plates were some of the earliest realistic depictions of the night sky.[208]

An Experiment on a Bird in the Air Pump (1768), by Joseph Wright of Derby

Baroque paintings typically used a darker color scheme than previous painting styles in Europe. From the 17th century, darkness took up larger areas of paintings on average.[209] Changes in the chemical composition of the paint itself and the development of new techniques for representing light led to the tenebrism style of painting. Tenebrism used stark, realistic depictions of light contrasted with darkness to create realistic depictions of night and darkness illuminated by moonlight, candles, and lamps.[210] The work of Baroque painters, like Caravaggio, who painted an entire studio black, was influenced by the alchemical concept of "nigredo", or blackness as connected to death and decomposition.[211][212] Dutch Golden Age painter Rembrandt recreated the dim light cast by early street lighting by layering translucent brown glazes.[213]

The Starry Night (1889), by Van Gogh

Impressionists represented darkness with shades of brown and blue based on the ideas that true black was not present in nature and that black had a deadening effect on the art.[214] Claude Monet notably avoided black paints.[215] Vincent van Gogh used heavy outlines between panes of color in his paintings, inspired by woodblock printing in Japan. This style, called cloisonné after the metalworking technique that embedded glass between dark lines of wire, was adopted by other painters like Paul Gauguin.[216] As night in Europe became more artificially lit, former railway worker John Atkinson Grimshaw became known for his vibrantly lit urban paintings.[208] In the modern era, painters have variously returned to archetypal symbols to capture the awe of night or painted scenes that emphasize how the modern city separates the viewer from the night sky.[208]

Abhisarika Nayika (c. 1800), by Mola Ram

Near Eastern artists initially rejected these techniques to depict shadow as hiding aspects of creation in shadows.[217] Mughal painters quickly incorporated techniques to depict night, twilight, and mists.[218] Under Emperor Akbar I, European materials and techniques were imported. Rajasthani paintings combined these with traditional styles and symbolism. Nayikas, depictions of women seeking romantic love, were a common subject and often included night as the setting for romance and peril.[219] Jesuit painter Giuseppe Castiglione brought Renaissance techniques for painting light and shadow to 17th-century China.[220] In pieces like One Hundred Famous Views of Edo, Hiroshige developed techniques to represent shadow and nocturnal light that became widespread in Japanese Meiji-era art.[221] Known for his crowd scenes lit by fireworks, Hiroshige had a strong influence on European painters.[222]

See also

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Notes

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Night

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Night is the period of natural darkness on occurring when a location on the planet's surface faces due to its , typically spanning from sunset to sunrise and enabling the visibility of celestial bodies such as and . This phenomenon results directly from at approximately 15 degrees per hour relative to the Sun, creating a diurnal cycle of approximately 24 hours, though the precise length of night varies by latitude and season owing to the planet's 23.44-degree . Biologically, night aligns with human and animal circadian rhythms, which regulate sleep-wake cycles, hormone secretion like , and physiological processes such as body temperature and , with disruptions from artificial exposure linked to impaired , mood disorders, and increased health risks. Historically and culturally, night has shaped human activity, from pre-electric era patterns of biphasic sleep and nocturnal fears reflected in to modern extensions via that enable urban but alter natural ecological balances, including navigation and predator-prey dynamics.

Etymology and Terminology

Linguistic Origins

The English word night derives from Old English niht, an umlauted variant of neaht or næht, denoting the dark period of the day. This form emerged in the pre-1150 Old English period and was inherited directly from Proto-Germanic *nahts, which carried similar connotations of darkness or the absence of light. Proto-Germanic *nahts reconstructs to the Proto-Indo-European root *nókʷts (or variant *nekwt-), a nominal stem signifying "night" or "evening," attested across Indo-European languages as early as the Bronze Age through comparative linguistics. Cognates of night appear widely in , including Dutch nacht, German Nacht, and Swedish natt, all tracing to the same Proto-Germanic source and preserving the phonetic shift from PIE. Beyond Germanic, the PIE root manifests in Latin nox (genitive noctis), nyx (νύξ), and naktám ("at night"), illustrating a shared inheritance among Indo-European branches without evidence of borrowing. These forms predate written records, with the earliest attestations in Hittite and Vedic texts around 1500 BCE, where derivatives denote nocturnal periods. Folk etymologies linking night to "not light" or conflating it with the numeral "eight" (PIE *oḱtṓw) lack philological support, as sound correspondences and semantic evolution do not align.

Definitions and Distinctions

Night denotes the phase of the 24-hour solar day during which a given point on Earth's surface is not illuminated by direct , occurring when the Sun's center is below the horizon. This period typically spans from sunset—defined as the moment the Sun's disappears below the horizon—to sunrise, the symmetric event in the morning, encompassing durations that vary by and due to Earth's and . In equatorial regions, nights average approximately 12 hours year-round, while at higher latitudes, they shorten in summer and lengthen in winter, with extremes like continuous daylight or darkness during polar summers and winters. Distinctions arise primarily between full night and the preceding and following twilight intervals, where indirect illumination from atmospheric scattering persists. Twilight subdivides into civil (Sun's center 0° to 6° below horizon, sufficient for most outdoor activities without artificial light), nautical (6° to 12°, allowing horizon visibility for ), and astronomical (12° to 18°, permitting of faint celestial bodies). True astronomical night commences at the end of evening astronomical twilight (Sun >18° below horizon) and concludes at the start of morning astronomical twilight, yielding the darkest conditions free of significant solar interference. In contrast, civil night—for regulatory purposes such as —begins at the end of evening civil twilight and ends at morning civil twilight's onset, excluding deeper twilight phases. Dusk specifically marks the evening's transitional darkening, often equated with the conclusion of civil twilight or the onset of nautical twilight, distinguishing it from broader twilight or the uniform darkness of night proper. Dawn mirrors dusk in the morning, with "twilight" serving as the generic term for both periods of penumbral light, while night excludes all such illumination thresholds. These delineations stem from geometric solar depression angles, calibrated against empirical models, rather than subjective visibility. In non-Earth contexts, analogous "nights" on other bodies like Mars follow similar solar geometry but differ in duration due to varying periods and axial tilts.

Astronomical Foundations

Earth's Rotational Dynamics

on its axis, directed from the geographic toward the , produces the daily cycle of day and night by alternately exposing different hemispheres to . This rotation occurs at an angular velocity of approximately 7.292 × 10^{-5} radians per second, completing one full turn relative to the in 23 hours, 56 minutes, and 4 seconds, termed the sidereal day. The slightly longer mean solar day of 24 hours accounts for Earth's orbital motion around the Sun, which advances its position by about 1 degree daily, requiring an additional rotation to realign with the Sun's apparent position. The axis of is inclined at 23.5 degrees to the plane of around the Sun, known as the obliquity of the . This tilt does not cause day and night but modulates the duration of nighttime periods seasonally: at higher latitudes, nights lengthen in winter when the axis tilts away from the Sun and shorten in summer when tilted toward it. Equatorially, day and night remain roughly equal year-round, each lasting about 12 hours, as the rotational dynamics symmetrically divide the illuminated and dark hemispheres. The boundary between these hemispheres, , sweeps across the surface at equatorial linear speeds up to 1,670 kilometers per hour due to rotation. Rotational dynamics also influence apparent celestial motions, with rising in the east and setting in the west as the turns eastward. This consistent periodicity underpins timekeeping systems, where local derives directly from the of the Sun relative to the meridian, advancing 15 degrees per hour in sync with . Variations in rotational speed, such as tidal slowing by about 2.3 milliseconds per century, subtly affect night lengths over geological timescales but remain negligible on human scales.

Twilight Phases and Duration

Twilight refers to the transitional periods of diffuse illumination following sunset or preceding sunrise, when the Sun lies below the horizon but atmospheric provides residual . It is categorized into three distinct phases based on the geometric position of the Sun's center relative to the horizon, as defined by the U.S. Naval Observatory: civil twilight occurs when the Sun is between 0° and 6° below the horizon, nautical twilight from 6° to 12°, and astronomical twilight from 12° to 18°. These thresholds correspond to practical visibility conditions: civil twilight allows for most outdoor activities without artificial lighting due to sufficient illumination; nautical twilight enables horizon visibility for , though celestial bodies are obscured near the horizon; and astronomical twilight provides near-total darkness suitable for observing faint celestial objects, as the approaches the brightness of full night. The duration of each twilight phase depends on the observer's latitude, the season, and the Sun's declination, primarily because the Sun's apparent path across the sky varies in inclination relative to the horizon. At equatorial latitudes, where the ecliptic intersects the horizon at approximately 90°, twilight phases are shortest, typically lasting 20 to 25 minutes for civil twilight year-round, as the Sun descends steeply. In mid-latitudes (around 40°), durations extend to 25-35 minutes for civil twilight, increasing in summer when the solar path is shallower due to higher declination, potentially reaching 40 minutes or more. Higher latitudes experience progressively longer twilights; for instance, at 60°, civil twilight can last 40-90 minutes, and during polar summers, the Sun may not descend beyond 18°, resulting in continuous or extended twilight without true night. Full astronomical darkness requires the Sun to drop below 18°, which fails in polar regions beyond about 66.5° latitude near the summer solstice, leading to phenomena like the midnight sun or white nights. These variations arise from Earth's 23.44° , which alters the Sun's maximum altitude and path angle seasonally, with durations calculable via formulas accounting for and the observer's position. Observers at benefit from standard definitions assuming negligible terrain effects, though mountains or atmospheric conditions can modify perceived durations slightly.

Variations on Other Celestial Bodies

On the , night persists for approximately 14 Earth days due to its sidereal rotation period of 27.3 days, synchronized with its around , resulting in prolonged darkness without an atmosphere to moderate temperatures, which plummet below 100 . This extended lunar night contrasts sharply with Earth's ~12-hour cycles, posing challenges for sustained surface operations as heat dissipates rapidly into . Mars experiences nights of about 12 hours, aligned with its 24.6-hour solar day (sol), though polar regions see extended darkness during winter, lasting up to half a Martian year (~334 sols) at the . The thin CO2 atmosphere provides minimal insulation, causing surface temperatures to drop to -133°C on average at night, or as low as -160°C, with frost forming due to . Venus's solar day spans 116.75 days, driven by its 243-day retrograde rotation exceeding its 224.7-day , yielding extended periods of at any surface point despite uniform high temperatures (~460°C) from its dense, reflective atmosphere that traps heat and scatters sunlight, blurring traditional day-night distinctions. Recent observations reveal distinct nighttime cloud dynamics, but surface illumination remains diffuse. Mercury's nights endure roughly 88 days within its 176-day solar day, stemming from a 3:2 spin-orbit with temperatures plunging to -180°C absent an atmosphere, enabling extreme diurnal swings from 430°C daytime highs as the surface radiates heat unchecked. 's major moons, tidally locked to the planet, exhibit day-night cycles matching their orbital periods around Jupiter—1.77 days for Io, 3.55 for Europa—where "night" denotes the hemisphere facing away from the Sun, often interrupted by Jupiter's reflected light or eclipses, though solar illumination dominates the primary rhythm. These variations underscore how , , and atmospheric presence dictate night's length and severity across celestial bodies.

Biological Mechanisms

Circadian Rhythms and Molecular Clocks

Circadian rhythms are endogenous, self-sustaining oscillations with a periodicity of approximately 24 hours that align physiological and behavioral processes to the Earth's light-dark cycle, enabling anticipation of environmental transitions such as the onset of night. In diurnal organisms, including humans, these rhythms promote wakefulness and metabolic activity during the light phase (day) while facilitating rest, reduced core body temperature, and hormone secretion like during the dark phase (night). The rhythms persist in constant conditions with a free-running period slightly deviating from 24 hours—typically 24.2 hours in humans—but entrain to the precise 24-hour geophysical day through zeitgebers, primarily the light-dark cycle. At the cellular level, circadian rhythms arise from molecular clocks comprising interlocking transcription-translation feedback loops (TTFLs) that generate oscillatory . In mammals, the positive arm involves the heterodimer of BMAL1 and CLOCK proteins binding to elements in promoters to drive transcription of Per (1, 2, 3) and Cry (1, 2) genes, along with accessory loops involving REV-ERB and nuclear receptors that regulate Bmal1 expression. The negative arm features accumulating PER and CRY proteins forming complexes that translocate to the nucleus, inhibiting BMAL1-CLOCK activity and repressing their own transcription; post-translational modifications, including by kinases like CK1ε and ubiquitination, facilitate protein degradation to reset the cycle every ~24 hours. These mechanisms, conserved from to mammals, were elucidated through genetic screens identifying period mutants in fruit flies in , followed by isolation of clock components, earning Jeffrey C. Hall, , and the 2017 in Physiology or Medicine. Molecular clocks operate autonomously in nearly every cell, but systemic coherence relies on the (SCN) in the as the master oscillator, which integrates photic input via the to phase-advance or delay peripheral clocks. Night's darkness permits accumulation of clock repressors during the subjective night, while light exposure during this phase suppresses them, preventing phase delays; disruption by artificial light at night desynchronizes rhythms, as evidenced by delayed onset and altered sleep timing in humans exposed to evening illumination. This entrainment ensures that during biological night, outputs such as reduced alertness and enhanced repair processes align with reduced environmental demands, underscoring the clock's adaptive role in energy conservation and survival.

Adaptations in Animals

Nocturnal animals, defined as those primarily active during the period of , have evolved specialized sensory, physiological, and behavioral traits to exploit low-light environments, often to evade diurnal predators, reduce for resources, or optimize in cooler temperatures. These adaptations vary across taxa but commonly emphasize non-visual senses alongside enhanced , as complete limits reliance on sight alone. For instance, many nocturnal vertebrates possess enlarged eyes with a predominance of rod photoreceptors, which detect dim through high sensitivity to single photons, enabling detection thresholds as low as 10^-5 in like the . A key optical feature in numerous nocturnal mammals and some birds is the , a iridescent, guanine-based layer posterior to the that reflects unabsorbed back toward the photoreceptors, potentially doubling or tripling capture efficiency and thus amplifying visual signals in mesopic conditions. This structure, absent in diurnal like humans, produces eyeshine via retroreflection and is documented in over 90% of terrestrial nocturnal mammal species examined, including carnivores such as cats (Felis catus) where it enhances prey detection at distances exceeding 100 meters under . Comparative anatomical studies confirm its role in boosting retinal illuminance without compromising acuity, though it may slightly reduce resolution due to . Auditory adaptations predominate in flying or fast-moving nocturnal species, exemplified by echolocation in bats (Chiroptera), where laryngeal emission of frequency-modulated ultrasonic pulses (20-200 kHz) allows precise three-dimensional mapping of obstacles and prey via echo delays and Doppler shifts, with resolutions down to centimeters. This system, which evolved convergently in the suborders and around 50-60 million years ago, correlates with enlarged cochleae and neural processing dedicated to high-frequency hearing, enabling prey capture success rates above 70% in cluttered forests. Owls (Strigiformes) complement vision with asymmetric ear positioning and facial ruffs that funnel sound, localizing prey buried under 20 cm of snow or leaves with errors under 1 degree azimuthally. Circadian rhythms in phase activity to the subjective night, driven by oscillators that invert the rest-activity cycle relative to diurnal counterparts, with peak release aligning to daylight exposure for entrainment. Molecular divergences, such as variant clock expressions (e.g., Per2 and Cry1), underpin this temporal niche partitioning, allowing sustained during dark phases while conserving energy via in small mammals like the , where metabolic rates drop 30-50% during inactive periods. These intrinsic clocks interact with extrinsic cues like moonlight intensity, modulating behaviors such as migration or to minimize predation risk. Behavioral strategies further reinforce physiological traits, including silent flight in via serrated wing feathers reducing noise by up to 10 dB, or scent-based in nocturnal prosimians with hypertrophied olfactory bulbs processing volatile cues over kilometers. Such multimodal integrations reflect evolutionary pressures favoring sensory redundancy in photon-scarce habitats, as evidenced by genomic analyses showing relaxed selection on cone opsins in lineages shifting to post-dinosaur extinction.

Responses in Plants and Microorganisms

Plants maintain endogenous circadian rhythms entrained by the day-night cycle, which regulate physiological processes such as leaf movements, , and metabolic shifts during . In the absence of , stomata in most C3 and C4 close partially or fully to conserve water, as continues via nocturnal conductance but without compensatory , optimizing whole-plant water use efficiency. Nighttime stomatal varies with environmental factors like deficit and , with higher conductance observed under humid conditions to facilitate CO2 uptake for respiration or growth, though this increases water loss risks. in relies on uninterrupted night length perception via photoreceptors; short-day (e.g., ) require nights longer than 10-12 hours to induce flowering, as demonstrated by night-break experiments interrupting with brief , which inhibits floral transition by reverting to its active form. also suppresses photosynthetic rates through circadian-mediated depression, with respiration dominating as catabolize stored carbohydrates accumulated during daylight. Microorganisms, particularly photosynthetic prokaryotes like , possess robust circadian clocks that anticipate and respond to nightly by reprogramming for survival. In elongatus, onset of triggers abrupt oxidation of in the , generating oxidized quinones that directly signal the core clock oscillator (KaiABC complex) to reset phase and initiate night-phase programs, such as halting and promoting breakdown for sustained . This clock ensures DNA replication initiates early in the subjective day to complete before nightly replication shutdown, preventing errors under dark conditions where repair mechanisms are downregulated; mutants with disrupted clocks exhibit replication stalling and reduced fitness. Cyanobacterial competence for DNA uptake, crucial for , peaks at night under clock control, adapting to seasonal night lengthening by extending the competence window. Non-photosynthetic , including species like Enterococcus faecalis, display circadian-like oscillations in and independent of , driven by host-associated rhythms mimicking day-night cycles, though these lack the full entrainment of cyanobacterial systems. In soil communities, stabilizes microbial diversity compared to constant , likely by reducing and aligning metabolic activity with exudation patterns.

Physiological and Health Effects

Natural Sleep Cycles and Restoration

Human sleep naturally aligns with the nocturnal period, driven by the , which promotes a consolidated episode typically lasting 7 to 9 hours in adults to allow completion of 4 to 6 ultradian cycles. Each cycle spans approximately 90 to 110 minutes, progressing from light NREM stage 1 (transitional wake-to-sleep, lasting 5-10 minutes) through denser NREM stages 2 and 3 (featuring sleep spindles and slow-wave activity for consolidation) into sleep, where brain activity resembles wakefulness but muscle atonia prevents movement. Early cycles emphasize deeper NREM for bodily maintenance, while later cycles allocate more time to , reflecting homeostatic sleep pressure accumulation over wakefulness interacting with circadian promotion of during darkness. Restoration during natural nighttime sleep occurs primarily through NREM (stage 3), where secretion peaks, facilitating protein synthesis, tissue repair, and metabolic regulation; this stage constitutes about 20-25% of total sleep in healthy adults. Concurrently, enhancement is evident, as production increases and T-cell activity strengthens, reducing vulnerability—evidenced by studies showing acute sleep restriction halves activity. REM sleep, comprising 20-25% of cycles, supports , emotional processing, and via theta waves and hippocampal replay, with deprivation impairing procedural learning and increasing reactivity to stressors. Circadian entrainment to the light-dark cycle optimizes this architecture via the , which suppresses alertness-promoting during night and signals pineal release in sustained darkness, peaking 2-4 hours before habitual wake time to deepen onset and efficiency. , dubbed the "hormone of darkness," not only lowers core body temperature to favor heat loss and propensity but also exerts antioxidant effects, mitigating accumulated during daytime activity. Empirical data from indicate that adherence to natural dusk-dawn timing yields superior slow-wave and REM proportions compared to misaligned schedules, correlating with enhanced recovery metrics like reduced markers (e.g., ) and improved glucose . Disruptions, such as even dim exposure, suppress by up to 50% and shorten perceived night duration, underscoring darkness's causal role in restorative fidelity.

Disruptions from Artificial Illumination

Artificial light at night (ALAN) primarily disrupts human physiology by suppressing the production of , a secreted by the in response to darkness that regulates circadian rhythms and sleep-wake cycles. Exposure to even low-intensity during typical sleep hours mimics daylight signals to the , the brain's master clock, thereby inhibiting synthesis and altering its circadian rhythmicity. Studies in blind individuals, who lack non-visual input to the circadian system, confirm that exposure directly suppresses independently of . This suppression impairs sleep architecture, increasing the time to fall asleep and reducing total sleep duration. Experimental evidence shows that bedroom light exposure during sleep correlates with shallower sleep stages and fragmented rest, as measured by . Population-level data link higher outdoor ALAN exposure to elevated symptoms, with cross-sectional analyses of queries indicating dose-dependent associations between light pollution intensity and sleep complaints. Beyond , chronic circadian misalignment from ALAN contributes to metabolic dysregulation, including increased risk. Longitudinal studies associate nighttime exposure with and higher , potentially via disrupted and signaling influenced by deficits. Similarly, the U.S. National Program's 2021 assessment found sufficient evidence linking LAN exposure to cancer development in humans, particularly , based on mechanistic and epidemiologic data showing modulation and proliferative effects from circadian disruption. Mental health outcomes are also adversely affected, with meta-analyses demonstrating that LAN exposure exacerbates depression and symptoms through sustained elevation and mood-stabilizing imbalances. These effects stem from the decoupling of internal clocks from environmental cues, leading to phase shifts that misalign physiological processes like immune function and release. While individual sensitivity varies by age, , and light spectrum—blue-enriched LEDs posing greater risks due to activation—collective evidence underscores ALAN as a modifiable in circadian-mediated pathologies.

Long-Term Health Consequences

Chronic disruption of natural nighttime darkness through , artificial exposure, or irregular patterns leads to misalignment of circadian rhythms, contributing to elevated risks of metabolic, cardiovascular, and oncologic diseases. The International Agency for Research on Cancer (IARC) classified as "probably carcinogenic to humans" (Group 2A) in 2020, citing limited evidence of increased incidence among long-term shift workers and sufficient mechanistic evidence involving suppression and clock gene dysregulation. Experimental and epidemiological data further link such disruptions to heightened risks of , colorectal, and gastrointestinal cancers, with prospective cohort studies showing dose-dependent associations for durations exceeding 10–20 years of night work. Exposure to artificial light at night (ALAN), including from indoor and outdoor sources, correlates with cardiometabolic disorders via persistent circadian desynchrony and reduced production. A 2024 meta-analysis of outdoor ALAN exposure reported increased odds of , , and , with hazard ratios ranging from 1.1 to 1.5 across cohorts. Long-term elevates cardiovascular event risks, including and , independent of traditional factors like , with relative risks up to 1.4 in meta-analyses of over 100,000 workers. Metabolic consequences include , , and , driven by altered glucose and regulation from chronic partial restriction. Longitudinal studies demonstrate that habitual sleep durations below 6 hours per night raise incidence by 50–89% and diabetes risk by 9–28% over 5–10 years, mediated by impaired sensitivity and elevated levels. These effects persist even after adjusting for confounders, underscoring circadian misalignment as a causal pathway rather than mere .

Societal and Technological Interactions

Historical Innovations in Illumination

The control of by early hominids, evidenced by burnt s and reddened sediments at sites like in dating to approximately 1 million years ago, marked the initial innovation in artificial illumination, enabling prolonged visibility and activity beyond daylight in shelters. More consistent habitual use emerged around 400,000 years ago with intact hearths, providing steady light from wood or fuels that extended social and survival tasks into darkness, though limited by smoke, short duration, and fire hazards. Oil lamps, utilizing animal fats or vegetable oils wicked through or stone reservoirs, originated in the and around 3500–3000 BCE, with mass-produced terracotta variants appearing by the BCE in , offering portable, soot-reduced light superior to open flames for tasks like writing and . These flat-wick designs burned for hours, illuminating households and temples, and spread via trade to , where bronze models enhanced efficiency, though they required frequent refilling and produced odors. Candles, formed by dipping or molding or around wicks, evolved from Egyptian rushlights around 3000 BCE but achieved practical form with Roman candles by 500 BCE, providing self-contained, drip-resistant illumination for indoor use without reservoirs. Chinese innovations in the (221–206 BCE) incorporated whale fat for brighter, longer-burning variants, while medieval refined them with for maritime signaling, though high cost and guttering limited widespread adoption until paraffin wax in the enabled cheaper production. These advancements incrementally compressed perceived night length in agrarian societies by supporting evening labor and study. Coal gas lighting, pioneered by Scottish engineer in 1792 through distillation and piping experiments at his Birmingham home, introduced brighter, adjustable flames via burners, first applied industrially in factories to extend production hours without daylight dependence. Public street installations followed in 1807 in , reducing crime and enabling nightlife in urban centers, with gasometers storing fuel for reliable supply, though explosion risks persisted until mantles improved safety in the . The incandescent electric bulb, developed by Thomas Edison's team with a high-resistance carbon filament vacuum-sealed in , achieved practicality on October 21, 1879, glowing for 13.5 hours initially and scaling to 1,200 hours by 1880, powered by central stations for flicker-free, ignition-free light. Patented January 27, 1880, it revolutionized illumination by centralizing generation and wiring homes, slashing fire risks from open flames and fostering 24-hour economies, as factories and cities operated continuously without seasonal light constraints. This shift, building on arc lights from the , fundamentally altered human by eroding natural night boundaries, with global adoption accelerating post-1900 via filaments.

Contemporary Nighttime Economies

The nighttime economy encompasses economic activities occurring between 6 p.m. and 6 a.m., primarily involving , , dining, , and related services that leverage extended hours to generate revenue and employment. These sectors have expanded in urban centers due to advancements in artificial and transportation, enabling 24-hour operations that contrast with traditional diurnal business models. In major cities, the nighttime economy contributes substantially to local (GDP) and job creation. For instance, New York City's nighttime activities generated $35.1 billion in annual value as of recent estimates, supporting approximately 300,000 jobs across and . In , it accounted for £26 billion in economic output, while the as a whole saw the sector represent 4.1% of national GDP in 2022, equating to £93.7 billion in revenue. Philadelphia's analysis for 2023 highlighted similar proportional impacts, with nighttime sectors driving visitor spending and tax revenues amid urban revitalization efforts. To manage growth and mitigate disruptions, over 80 cities worldwide have appointed "night mayors" or equivalent roles focused on nighttime governance, balancing economic vitality with public safety and infrastructure demands. pioneered such positions with policies like 24-hour venue licensing to sustain while addressing and transport needs. These officials coordinate with stakeholders to optimize public transit extension, lighting, and event permitting, as seen in London's night czar initiatives that promote diversified late-night offerings beyond alcohol-centric venues. Such strategies have proven effective in fostering inclusive 24-hour urbanism, though empirical evaluations emphasize the need for data-driven adjustments to avoid over-reliance on amid shifting consumer behaviors post-2020.

Safety, Crime Patterns, and Risk Factors

Empirical studies consistently demonstrate that crime rates, particularly for violent offenses such as and , are elevated during nighttime hours compared to daylight. For instance, analysis of police-recorded crimes in indicates that transitioning from full daylight to full significantly increases the predicted volume of robberies, with darkness serving as a key enabling factor. Similarly, registered report protocols examining temporal crime data have found odds ratios greater than one for specific crimes occurring after dark versus during daylight, confirming heightened in low-light conditions. These patterns hold across urban settings, where assaults in departments double on preceding work-free days, correlating with extended evening activities. Causal mechanisms underlying these patterns include reduced natural and visibility, which lower the perceived risk of detection for offenders while complicating victim resistance or escape. posits that facilitates opportunistic crimes by minimizing guardianship—fewer witnesses or passersby—and increasing the anonymity of perpetrators. Empirical evidence from transitions, which extend ambient light into evenings, supports this: such policy shifts reduce robbery rates by approximately 7%, with stronger effects in areas of higher baseline crime. However, some observational data suggest variability; for example, certain bright urban areas may still exhibit elevated crime due to concentrated activity, though overall amplifies incidence beyond activity levels alone. Individual risk factors for nighttime victimization prominently feature alcohol consumption, which impairs judgment and physical coordination, thereby elevating vulnerability to assaults and . In , self-reported data from 2014 linked higher alcohol use to increased violent victimization rates, independent of other demographics, with settings amplifying exposure. Prolonged outings in public venues, such as bars during night-time economies, further compound risks, as extended duration and venue-hopping correlate with higher odds of violent encounters. are particularly susceptible, with alcohol-fueled impulsivity and gang-related activities peaking nocturnally, per global health analyses. Demographic factors like age and location (urban streets versus rural areas) modulate these risks, but and intoxication remain proximal causes across groups. Mitigation strategies, notably improved street , demonstrably curb nighttime through enhanced deterrence and . A meta-analysis of 17 rigorous studies found that street lighting interventions yield a statistically significant 14% reduction in overall , with pronounced effects on and violent offenses in public spaces. Randomized experiments in U.S. cities corroborate this, reporting up to 36% drops in outdoor index crimes post-installation, even accounting for spillovers to adjacent areas. Conversely, selective evidence from lighting reductions (e.g., part-night dimming) shows minimal crime upticks, suggesting thresholds where baseline illumination suffices, though comprehensive reviews affirm net benefits from sustained lighting for .

Psychological and Evolutionary Perspectives

Innate Human Responses to Darkness

Darkness triggers the human to secrete , a that promotes sleepiness and aligns physiological processes with the , peaking during prolonged absence of cues. This response evolved in diurnal , including humans, to synchronize rest with periods of reduced visibility and activity, minimizing energy expenditure when or defense is impaired. onset serves as an internal marker of night, suppressing during exposure and facilitating phase alignment of the , the brain's master clock. Physiologically, exposure to darkness induces mydriasis, or pupil dilation, to maximize light intake via rod photoreceptors, enabling scotopic vision adapted for low luminance but with diminished color and acuity compared to photopic conditions. This adaptation, while innate, underscores vulnerability: human visual acuity drops sharply below 0.01 lux, heightening reliance on other senses like audition for threat detection. Concurrently, darkness modulates innate immune responses, with studies in model organisms showing altered baseline immunity and inflammatory profiles under constant dark versus light cycles, suggesting conserved mechanisms in humans for nocturnal repair processes. Evolutionarily, innate fear responses to darkness—manifesting as nyctophobia in extreme cases—arise from impaired , where low obscures predators or hazards, prompting avoidance behaviors as a optimization strategy. In an evolutionary framework, this fear functions adaptively by restricting movement during high-risk periods, akin to nocturnal predator evasion in ancestral environments, with hyperactivity amplifying uncertainty in unseen spaces. Empirical evidence from cross-cultural studies indicates higher prevalence in children, diminishing with experience but rooted in hardwired neural circuits prioritizing caution over exploration in obscurity. Behavioral assays confirm elevated and in dark conditions, reflecting sympathetic activation independent of learned associations.

Cultural Conditioning Versus Biological Imperatives

Humans possess an innate biological drive to align activity with diurnal cycles, governed by circadian rhythms that promote wakefulness during daylight and during to optimize , predator avoidance, and physiological restoration. These rhythms, conserved across species from to mammals, evolved in response to solar entraining cues like , enabling anticipation of environmental shifts in , availability, and . Evolutionarily, nighttime likely emerged as an adaptive to minimize to nocturnal threats, with genetic mechanisms hardwiring physiological changes that reduce activity and enhance restorative processes during dark hours. An associated imperative is nyctophobia, or fear of , which stems from ancestral selection pressures favoring heightened vigilance against predators active at night, as evidenced by physiological responses like increased and in low-light conditions. Cultural conditioning, amplified by industrialization and electrification since the , increasingly overrides these imperatives through extended illumination and economic incentives for nocturnal productivity. Pre-industrial societies typically segmented sleep into two phases aligned with sunset and sunrise, averaging 6-8 hours total, but artificial disrupted this pattern, fostering segmented wakefulness and later bedtimes. , prevalent in 15-20% of modern workforces, exemplifies this override by enforcing arousal during biologically optimal windows, leading to chronic circadian misalignment. Urban environments further condition individuals to embrace nighttime and , with street and venues diminishing perceived , yet surveys indicate 11-28% of adults retain discomfort sleeping in unlit conditions, reflecting unresolved evolutionary residues. The tension manifests in measurable detriments when culture supersedes biology, as prolonged exposure to night work elevates risks of metabolic disorders, , and by suppressing and desynchronizing hormonal cycles. A 2022 meta-analysis linked to 40% higher incidence of coronary heart disease, attributing to disrupted architecture rather than confounding factors alone. Despite these costs, societal structures prioritize output over alignment, with minimal accommodations like dimmed lighting or napping protocols proving insufficient to fully mitigate impairments. posits that while cultural adaptation enables flexibility—such as through fire and later —persistent biological signals, including innate aversion to unseen threats, underscore limits to such overrides, as modern safety nets do not eradicate subconscious alerts honed over millennia.

Cultural and Religious Contexts

Mythological Narratives

In , embodies the night as a primordial born from Chaos, as detailed in Hesiod's composed circa 700 BCE. She unions with , the darkness, to birth (day), Aether (bright upper sky), and numerous chthonic entities such as the (doom-bringers), (doom), (death), (sleep), the Oneiroi (dreams), the , and the (fates). 's veil of darkness holds immense power; in the attributed to around the 8th century BCE, refrains from harming her son after threatens retribution, underscoring her feared autonomy even among Olympians. Norse mythology personifies night through Nótt, a jötunn goddess tracing her lineage in Snorri Sturluson's Prose Edda (13th century CE, drawing from older oral traditions). Nótt, riding her horse Hrímfaxi whose mane drips dew and frost, circles daily, alternating with her son (day) whose horse Skinfaxi illuminates the sky. The gods grant Nótt the horse and pledge support to her kin, including her daughter Jörd (earth, mother of Thor), establishing cosmic rhythm in narratives like . Nótt symbolizes repose and the veil between worlds, invoked in Eddic poetry for protection against nocturnal perils. In Egyptian cosmology, Nut represents the star-strewn , depicted as a woman arched over earth-god , separated by air-god Shu in myths from the (circa 2400–2300 BCE). Each evening, Nut swallows the sun god , traversing her body to rebirth him at dawn, ensuring daily renewal as recounted in (circa 2100 BCE). This narrative underscores night's role in regeneration, with Nut's starry belly embodying celestial order and protection over the deceased in the underworld journey. Hindu Vedic traditions invoke as the goddess of night in the Rigveda (circa 1500–1200 BCE), hymned alongside her sister (dawn) for safeguarding against demons and thieves during vulnerability. , dark-complexioned with star adornments, bestows rest and prosperity, personifying night's dual benevolence and peril; hymns like RV 10.127 portray her extending protective wings, warding evil while facilitating cosmic balance with day. Among Mesoamerican , night features in the tonalpohualli calendar's , deities cycling every nine days to govern fate, as described in 16th-century codices like the . , "Smoking Mirror," associates with the , sorcery, and prowls, embodying nocturnal unpredictability and rulership in myths where he topples solar gods in cosmic battles. These lords, starting with (fire), influence and rituals, framing night as a realm of hidden forces and potential catastrophe.

Religious Practices and Symbolism

In , night often symbolizes spiritual darkness representing ignorance, sin, and the present age of evil, contrasted with the light of divine revelation and the coming day of salvation. Practices include the , with as the night prayer emphasizing protection from nocturnal temptations and rest in God's care, rooted in monastic traditions from the early Church. The "," described by mystics like St. John of the Cross in the , denotes a phase of spiritual purification involving detachment from consolations, leading to deeper union with God. In Islam, night holds profound significance through practices like the Isha prayer, the final obligatory salah performed after twilight, and Tahajjud, voluntary night vigils recommended in the Quran for intimate communion with Allah. Laylat al-Qadr, the Night of Power observed during the last ten nights of Ramadan—traditionally the 27th—commemorates the Quran's revelation and is deemed superior to a thousand months, with Muslims engaging in extended prayer, Quran recitation, and supplication (dua) seeking forgiveness and mercy. Pre-sleep rituals include reciting dhikr such as Subhanallah, Alhamdulillah, and Allahu Akbar thirty-three times each, emulating the Prophet Muhammad's sunnah to invoke protection and gratitude. Judaism views the day commencing at nightfall, reflecting the Genesis creation account where evening precedes morning, symbolizing a transition from divine judgment (gevurah) in the night's first half to mercy in the latter. Night evokes exile and suffering, with dawn heralding redemption, as in Passover narratives; kabbalistic traditions associate darkness with restriction or evil, yet also opportunities for mystical study. Observances include the Shema prayer recited at night for spiritual safeguarding and all-night Torah study (Tikkun Leil Shavuot) on Shavuot, commemorating the revelation at Sinai, practiced widely since medieval times to emulate the angels' ceaseless praise. In , night symbolizes dissolution and stillness akin to cosmic during Brahma's night, representing death and the cessation of activity, while festivals like entail all-night vigils of fasting, meditation, and worship to seek destruction of ego and attainment of . , spanning nine nights, honors Durga's forms culminating in victory over darkness, with devotees performing aarti and dances; cremations avoid nighttime due to beliefs in heightened negative energies. Buddhist traditions emphasize night for contemplative practices, including sleep in to cultivate lucidity in dreams and maintain awareness across sleep states, dividing the night into segments for virtue, practice, and rest as advised in texts like those of Lama Zopa Rinpoche. Evening routines involve and precepts recitation in monasteries, fostering to counter or restlessness, with the Buddha's enlightenment under the Bodhi tree occurring at night, underscoring darkness as a backdrop for profound insight.

Artistic and Media Depictions

Literary Explorations

In , night has long served as a multifaceted symbol encompassing mystery, peril, introspection, and renewal, often contrasting with the clarity of day. Ancient texts personified night as a divine entity, such as in , depicted driving a chariot across the sky, embodying both the veil of obscurity and the precursor to dawn. This portrayal underscores night's role as a liminal space where human agency confronts the unknown, facilitating narratives of heroism or dread, as seen in Homeric epics where nocturnal journeys test resolve. Medieval works extended these motifs into allegorical debates and moral reckonings, exemplified by the 13th-century poem , where nocturnal creatures engage in philosophical contention under night's shroud, symbolizing contemplative discord amid natural order. drama amplified night's dramatic potential for intrigue and the ; William Shakespeare's (c. 1595–1596) unfolds much of its enchanted chaos during night, with fairies exploiting darkness for mischievous interventions in human affairs, highlighting themes of versus . Similarly, in (1606), night cloaks and apparitions, intensifying moral and fate's inexorability. Romantic poets reframed night as a domain of sublime escape and existential meditation. ' "" (1819) immerses the speaker in night's embrace, drawn to the bird's song as a portal beyond "weariness, the fever, and the fret" of human life, culminating in a desire to "cease upon the midnight with no pain." Here, night evokes through art's timelessness, juxtaposed against mortal decay, reflecting Keats' preoccupation with transience amid sensory immersion. In the 20th century, ' villanelle "Do Not Go Gentle into That Good Night" (1951) equates night with death's inevitability, imploring defiance: "Rage, rage against the dying of the light," portraying night not as respite but as an adversary to vital force. Modern prose often harnesses night to probe psychological and historical abysses. Elie Wiesel's Night (published in Yiddish as Un di velt hot geshvign in 1956; English translation 1960) deploys perpetual night as emblematic of Holocaust-induced despair, where darkness signifies divine absence and dehumanization, drawn from Wiesel's Auschwitz experiences beginning in 1944. This usage aligns with broader modernist tendencies to view night as a for inner turmoil, as in Edgar Allan Poe's tales where it amplifies gothic horror and subconscious fears. Across eras, literature leverages night's empirical opacity—absence of light enabling unseen threats or revelations—to explore causal tensions between , individual will and cosmic indifference.

Visual and Cinematic Representations

In visual arts, depictions of night, often termed nocturnes, emerged prominently in the Dutch Golden Age with artists like Aert van der Neer, who painted moonlit landscapes emphasizing subtle light contrasts from the moon and reflective surfaces to convey serene yet mysterious atmospheres in the 17th century. By the 19th century, Post-Impressionist Vincent van Gogh advanced nocturnal representations through works such as Starry Night Over the Rhône (1888), capturing an unpolluted starry sky over Arles, France, with deliberate starry reflections on the water to highlight natural luminosity absent in modern urban settings. His The Starry Night (June 1889), created during a stay at the Saint-Paul-de-Mausole asylum, features a swirling, turbulent night sky dominated by a crescent moon and Venus, shifting from representational accuracy to expressive mood through bold brushstrokes and heightened color contrasts. Cinematic representations of night frequently leverage darkness to amplify psychological tension and visual drama, particularly in the film noir genre that arose in American cinema during the 1940s and 1950s, characterized by , deep shadows, and urban night scenes evoking moral ambiguity and existential dread. Cinematographers employed high-contrast black-and-white techniques, such as effects from neon signs and streetlights on rain-slicked streets, to symbolize isolation and peril, as seen in films like (1946), where nocturnal alleys underscore narrative intrigue. These visual strategies, influenced by German Expressionism, exploit night's obfuscation of details to blur distinctions between and , enhancing thematic explorations of human vulnerability. In broader cinema, night settings in horror genres intensify innate fears of the unknown by limiting visibility, prompting reliance on auditory cues and sudden illuminations for .

Environmental Implications

Light Pollution Mechanics

Light pollution arises mechanically from the emission of artificial light at night that exceeds natural levels, primarily due to inefficient fixtures directing photons upward or outward rather than solely toward intended targets. Poor shielding on luminaires allows light to escape vertically, where it interacts with the atmosphere, undergoing processes that redistribute it across the and ground. This misdirection stems from design flaws in common sources such as streetlights, building facades, advertising displays, and sports arena floodlights, which collectively emit visible inefficiently. The core physical mechanism producing , the diffuse brightening of the above populated areas, involves single and multiple of upward-emitted light by atmospheric constituents. Rayleigh dominates for molecular interactions (e.g., and oxygen), with intensity scaling as λ^{-4} (favoring shorter wavelengths), while Mie applies to larger aerosols like and pollutants, which extend the effect to longer wavelengths and enhance overall radiance. Air increases aerosol density, amplifying efficiency, and clouds can reflect and redirect light, boosting by factors up to 1000 compared to clear conditions. Empirical models, such as Walker's Law (skyglow radiance proportional to local divided by distance to the power of -2.5), quantify this dependency on source proximity and intensity. -rich spectra from modern LEDs exacerbate Rayleigh , contributing disproportionately to relative to traditional sodium lamps. Glare occurs when unshielded or overly bright sources emit direct, high-intensity beams that overwhelm the eye's , reducing contrast sensitivity and causing discomfort through excessive without atmospheric mediation. This mechanic relies on the for light falloff but is worsened by specular reflections from surfaces, creating disability glare that impairs . Light trespass involves the direct propagation of light beyond its target area, often via horizontal or tilted beams from fixtures lacking full , intruding into adjacent spaces like bedrooms or natural habitats without . This is governed by basic geometric and , with trespass intensity diminishing with distance squared absent intervening media. Clutter emerges from the spatial density of multiple overlapping sources, producing a chaotic visual field where cumulative illuminance from glare, trespass, and minor skyglow components confounds perception, though it lacks a dominant scattering mechanic and instead reflects aggregate emission patterns in dense urban settings.

Ecological and Biodiversity Consequences

Artificial light at night (ALAN) disrupts nocturnal ecosystems by altering sensory cues, circadian rhythms, and interspecies interactions, contributing to declines across taxa. Empirical studies document increased mortality, behavioral maladaptations, and reduced reproduction, with ALAN levels rising at an estimated 9.6% annually in high- areas. These effects cascade through food webs, amplifying and loss. Insects, foundational to food chains, experience mass attraction to lights, leading to exhaustion, predation, and direct mortality; this , observed in moths and other nocturnal , correlates with declines, such as 34% of common macro-moths in showing significant reductions linked to light exposure. ALAN suppresses and , reducing available to predators and disrupting dynamics. Quantitative field experiments confirm that even low-intensity lighting halves activity in affected zones. Avian species suffer disorientation during migration, with lights causing fatal collisions into structures; estimates indicate hundreds of millions of birds die annually in alone from this trap. Nocturnal migrants alter flight paths around lit urban areas, increasing expenditure and predation risk. Mammals like bats exhibit avoidance of illuminated habitats, reducing efficiency and creating barrier effects that fragment landscapes and limit . Small mammals show suppressed production, altering reproduction and immune function. Marine ecosystems face parallel disruptions, particularly for sea turtles, where coastal ALAN misorients hatchlings away from the sea, resulting in desiccation and predation; studies report up to 95% disorientation rates on lit beaches. Fish and plankton exhibit shifted vertical migrations, altering trophic interactions. Plants respond to extended photoperiods with delayed dormancy or mistimed flowering, desynchronizing with pollinators and herbivores, though data remain sparser compared to faunal impacts. Overall, ALAN exacerbates other stressors like climate change, with meta-analyses underscoring its role in global biodiversity erosion.

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