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Solar viewer
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Solar viewers (also known as solar viewing glasses or solar eclipse glasses) are special eyewear designed for direct viewing of the Sun. Standard sunglasses are unable to filter out eye-damaging radiation. Solar viewers can be used for safe viewing of solar events such as eclipses. The recommended optical density of this eyewear is 5, meaning that the solar viewing filter only permits 1 part in 100,000 of incident light to pass through. In addition to blocking visible light, solar viewers also block ultraviolet and infrared rays which can damage one's eyes.
Safety
[edit]According to the American Astronomical Society (AAS), products meeting the ISO 12312-2 standard are safe for direct solar viewing. The AAS maintains web pages giving detailed information about safe solar viewers[1] and a list of reputable vendors of eclipse glasses.[2] The organization warned against products claiming ISO certification, or even citing the exact standard number, but not tested by an accredited laboratory, or those bearing incomplete certification information. Another problem was counterfeits of reputable vendors' products, some even claiming the company's name (such as with American Paper Optics, which published information detailing the differences between its glasses and counterfeits).
Solar viewers manufactured prior to 2015 may have a three-year limit before they can no longer effectively filter out UV radiation and should no longer be used. Starting in 2015, products manufactured to meet the standards of ISO 12312-2 can be used indefinitely as long as they have not been damaged by scratches or tears.[3]
Solar viewers should be used for safe viewing of the Sun during partial solar eclipses and during the partial phases of a total solar eclipse event, when the Moon only covers a portion of the Sun's surface. Only during the brief period of totality of a total solar eclipse is it safe to view the Sun directly with the naked eye.
Counterfeit eclipse glasses
[edit]In the months leading to the solar eclipse of August 21, 2017, counterfeits of light-filtering glasses for solar eclipses began proliferating. Effective eclipse glasses filter visible, ultraviolet, and infrared light.[4] The eye's retina lacks pain receptors, and thus damage could occur without one's awareness.[5][6]
The AAS said determining whether an eclipse viewer was safe required a spectrophotometer and lab equipment, but often the user should see nothing through the filter except for the Sun, sunlight reflecting off shiny metal, or intense light sources such as an LED flashlight.[7]
Andrew Lund, the owner of a vendor of eclipse glasses, noted that not all counterfeit glasses were necessarily unsafe. He stated to Quartz that the counterfeits he tested blocked the majority of harmful light, concluding that "the IP is getting ripped off, but the good news is there are no long-term harmful effects."[4]
On July 27, 2017, Amazon required all eclipse viewing products sold on its website have a submission of origin and safety information, and proof of an accredited ISO certification. In mid-August 2017, Amazon recalled and pulled listings for eclipse viewing glasses that "may not comply with industry standards", and gave refunds to customers who had purchased them.[8][7]
On April 8, 2024, the Illinois Department of Public Health issued a recall on specific brands of eclipse glasses that failed to meet proper safety standards.[9]
See also
[edit]References
[edit]- ^ "How Can You Tell If Your Eclipse Glasses or Handheld Solar Viewers Are Safe?". American Astronomical Society. 23 February 2017. Archived from the original on 21 September 2022. Retrieved 13 February 2024.
- ^ "Suppliers of Safe Solar Viewers & Filters". American Astronomical Society. 11 January 2024. Archived from the original on 12 February 2024. Retrieved 13 February 2024.
- ^ Weisberger, Mindy (2017-08-25). "Will Your Solar Eclipse Glasses Still Be Safe to Use in 2024?". Live Science. Archived from the original on 2017-08-27. Retrieved 2017-08-28.
- ^ a b Wolfson, Elijah (July 27, 2017). "Solar-eclipse fever means counterfeit glasses are flooding Amazon's market". Quartz. Archived from the original on September 23, 2022. Retrieved August 19, 2017.
- ^ "How to Tell If Your Eclipse Glasses or Handheld Solar Viewers Are Safe". Solar Eclipse Across America – August 21, 2017. American Astronomical Society. February 23, 2017. Archived from the original on September 21, 2022. Retrieved August 20, 2017. Includes photos of genuine and fake eclipse glasses.
- ^ Pittman, Travis (August 18, 2017). "Here's How Fast Your Retina Could Burn Looking at Eclipse Unprotected". Denver, Colorado: 9 News.
- ^ a b "Amazon offers refunds to customers who bought fake eclipse glasses". CBC News. August 15, 2017. Archived from the original on September 22, 2022. Retrieved August 19, 2017.
- ^ Elliott, Matt (August 19, 2017). "How to tell if your solar eclipse glasses are safe or fake". CNET. Archived from the original on February 7, 2021. Retrieved August 19, 2017.
- ^ "Solar eclipse glasses sold through Amazon recalled, Illinois Department of Public Health says". ABC7 Chicago. 2024-04-08. Retrieved 2024-04-09.
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Solar viewer
View on Grokipediafrom Grokipedia
A solar viewer is a specialized device designed for the safe observation of the Sun, protecting the eyes from intense ultraviolet, visible, and infrared radiation that can cause permanent damage, particularly during solar eclipses or routine solar viewing.[1] These viewers encompass both direct filtered eyewear, such as eclipse glasses or handheld solar viewers compliant with the ISO 12312-2 international standard, and indirect projection methods like pinhole projectors.[1][2]
Direct solar viewers function by incorporating high-density filters that transmit only a small fraction of visible light—typically around 0.001% (optical density of about 5)—while blocking harmful wavelengths, allowing users to gaze at the Sun without risk except during the brief totality phase of a total eclipse.[2] These devices must be inspected for scratches, tears, or punctures before use, and they are unsuitable for viewing through cameras, binoculars, or telescopes without additional solar filters.[1] Handheld solar viewers, often distributed at educational events, provide portable protection and are recommended for partial and annular eclipse phases.[2]
In contrast, indirect solar viewers rely on projection to create an image of the Sun on a surface, eliminating direct exposure altogether.[3] The simplest form is the pinhole projector, constructed from everyday materials like cardboard, aluminum foil, and white paper, where sunlight passes through a tiny aperture to form an inverted image; the smaller the hole, the sharper the projection.[4] More advanced optical projections use telescopes or binoculars to magnify and display the solar disk on a screen, but users must never look through the optics at the Sun.[3] Both types emphasize that no direct staring at the Sun is ever safe without certified protection, and skin safeguards like sunscreen remain essential during prolonged outdoor exposure.[1]
where is the transmittance, the ratio of transmitted to incident light intensity. For safe direct solar observation, filters must achieve OD in the visible spectrum (400–700 nm), corresponding to or transmittance of at most 0.001%, which blocks 99.999% of visible light and prevents retinal overload.[34][35] Filters vary by type to suit different observational needs: neutral density filters provide broadband attenuation across the visible spectrum for general white-light viewing, while selective filters, such as H-alpha types, transmit a narrow band centered at 656.3 nm—the wavelength of hydrogen-alpha emission—to reveal red prominences and chromospheric features against a darker background. Materials commonly used include black polymer films embedded with carbon particles for primary absorption, yielding a yellow-orange solar image, and coated glass substrates that combine reflection from metallic layers (e.g., aluminum) with absorption for enhanced durability.[35][36][32] To address specific hazards, solar filters rigorously block ultraviolet (UV) wavelengths below 400 nm and infrared (IR) above 700 nm; UV blocking mitigates photochemical damage, including the blue-light hazard that triggers damaging chemical reactions in retinal cells, while IR blocking prevents thermal injury from heat buildup in eye tissues. Compliance with standards like ISO 12312-2 ensures UV transmittance below 0.0032% (e.g., 0.00000015%–0.0000026% for UVB at 280–315 nm) and IR transmittance around 0.01%–1.29% (700–2000 nm), far exceeding visible light attenuation.[37][35] Performance metrics for direct viewers emphasize low transmission rates, typically 0.00004%–0.0012% luminous transmittance to balance visibility and safety, with darker filters (e.g., OD >5.9) preferred for comfort during prolonged observation. Filter integrity can degrade over time due to physical damage like scratching, which scatters light and reduces OD, or delamination in polymer films, creating pinholes that allow unfiltered light to bypass attenuation and pose risks. Regular inspection for defects larger than 0.2 mm or clustered imperfections is essential to maintain efficacy.[35][37] These mechanisms underpin direct optical viewers and specialized devices by reducing solar intensity without distorting essential image details.[32]
Overview
Definition and Purpose
A solar viewer is a device or method engineered to enable safe observation of the Sun's disk, corona, or related phenomena by attenuating harmful portions of the solar spectrum, including ultraviolet (UV), infrared (IR), and excessive visible light, thereby preventing direct exposure to the eye.[5] These tools, such as specialized glasses or projection systems, reduce incoming solar intensity to levels that protect the retina while allowing visibility of solar features.[1] The primary purpose of solar viewers is to safeguard against solar retinopathy and other ocular injuries caused by solar radiation, ensuring users can engage in astronomical activities without risk of permanent vision loss.[6] They facilitate applications in astronomy education, where students learn about solar dynamics; public events like solar eclipses, promoting widespread safe participation; and amateur scientific observation, allowing documentation of solar activity.[1] Solar radiation spans the electromagnetic spectrum, encompassing UV-A (315–400 nm), UV-B (280–315 nm), UV-C (<280 nm, largely absorbed by the atmosphere), visible light (400–700 nm), and IR (>700 nm), with the Sun emitting intense energy across these bands that can penetrate the eye.[6] Unprotected viewing leads to photochemical damage from UV and blue-violet light, which generates reactive oxygen species damaging retinal cells, and thermal damage from IR and red-yellow light, which heats and coagulates retinal tissue, often resulting in irreversible scotomas or reduced acuity within seconds of exposure.[6] Solar viewers permit safe observation of events such as total and partial solar eclipses, where the Moon partially obscures the Sun; sunspots, dark regions on the photosphere visible during low solar activity; and solar flares, brief eruptions of energy, though direct viewing of intense flares requires additional equipment to limit exposure time.[7]Historical Context
Early methods for viewing solar eclipses relied on rudimentary techniques to mitigate the risk of direct exposure to intense sunlight. Prior to the 20th century, observers commonly used smoked glass, created by holding glass over a candle flame to deposit a layer of soot, or black glass to dim the sun's brightness sufficiently for partial viewing.[8] Natural projections, such as observing the sun's image through gaps in tree leaves or interlaced fingers, provided a safer indirect method by exploiting the pinhole effect to project the eclipse onto surfaces without eye strain.[9] These approaches, while innovative for their time, offered inconsistent protection and were prone to failure if the dimming was inadequate. Key milestones in solar viewing technology emerged in response to growing scientific interest in astronomy. The pinhole projector, an evolution of the ancient camera obscura principle first described by Ibn al-Haytham in the 11th century, was refined and popularized in the 19th century for safe eclipse observation, allowing projected images on screens without direct gazing.[9] In the 1970s, advances in materials led to the development of aluminized Mylar filters, thin polyester films coated with aluminum to reflect harmful solar radiation while transmitting a visible image, marking a shift toward more reliable direct-viewing options.[10][11] The adoption of the ISO 12312-2 international standard in 2015 formalized requirements for solar filters and eclipse glasses, ensuring they block at least 99.999% of intense visible light and nearly all ultraviolet and infrared radiation to prevent retinal damage.[12] Notable events underscored the need for improved safety measures. During the 1918 total solar eclipse crossing the United States, widespread use of unverified methods like smoked glass was common, though such methods are now known to provide inadequate protection against eye damage.[13] Commercialization accelerated in the late 20th century, with companies like American Paper Optics beginning production of affordable cardboard eclipse glasses in 1991, making certified viewers accessible for mass use.[14] The 2017 North American total solar eclipse, visible to over 200 million people, drove unprecedented distribution efforts, with manufacturers producing and supplying tens of millions of ISO-compliant glasses through schools, libraries, and retailers to avert widespread injuries.[15] The evolution of these technologies was propelled by advances in materials science, such as polymer films and metallic coatings, alongside heightened public health awareness following documented cases of painless but permanent eye damage from unprotected viewing.[16] Incidents of solar retinopathy during eclipses, which can manifest hours or days later without immediate pain due to the retina's lack of pain receptors, reinforced the push for standardized, evidence-based protections.[17] The April 8, 2024, total solar eclipse, visible across parts of Mexico, 15 U.S. states, and Canada, further demonstrated the importance of certified viewers, with tens of millions distributed to the public.[18]Types
Direct Optical Viewers
Direct optical viewers enable personal, line-of-sight observation of the Sun through specialized filtered eyewear, primarily designed for safe viewing of solar eclipses or partial solar phenomena.[12] These devices, such as eclipse glasses and solar binoculars, incorporate neutral density filters to attenuate intense solar radiation while preserving a discernible image.[19] Eclipse glasses typically feature thin lenses constructed from polyester or polycarbonate substrates coated with materials like chromium or aluminum to achieve an optical density (OD) of approximately 4.5 or greater in the visible spectrum (380–780 nm).[19] The ISO 12312-2 standard, adopted in 2015 and affirmed in 2020, remains current as of 2025 with no major updates.[12] This coating ensures high uniformity and minimal defects, such as pinholes larger than 200 μm, in compliance with ISO 12312-2 standards for solar viewers.[12] Solar binoculars employ similar neutral density filters mounted on the objective lenses, adapting the same filtration principles for magnified direct viewing without additional projection.[19] These viewers function by blocking approximately 99.999% of visible light, transmitting only about 0.001% to produce a neutral, low-contrast image of the solar disk suitable for brief observations.[12] They also attenuate nearly 100% of harmful ultraviolet (UV) radiation and at least 97% of infrared (IR) radiation, reducing the risk of retinal damage during partial solar events.[19] However, they are recommended for brief sessions to minimize eye strain and account for potential filter inconsistencies.[12] Advantages of direct optical viewers include their portability, as they require no external equipment, and affordability, with eclipse glasses often costing under $5 per pair from certified suppliers. Limitations arise from potential filter degradation over time, such as coating scratches or pinhole formation, necessitating inspection before each use and adherence to ISO 12312-2 certification for safety.[19]Projection-Based Viewers
Projection-based viewers utilize indirect methods to project an image of the Sun onto a surface, allowing safe observation without direct exposure to solar radiation. These devices operate on the camera obscura principle, where sunlight passes through a small aperture to form an inverted image on a screen or wall. The core method involves creating a pinhole with a diameter typically between 0.5 and 2 millimeters, which acts as a simple lens to focus light rays and produce a clear projection of the Sun's disk. This approach ensures no harmful light enters the eye, making it suitable for viewing partial solar eclipses or the Sun's general features. Common variations include simple cardboard projectors, such as a two-card setup where one card has a foil-covered pinhole and the other serves as a viewing screen held at a distance. Household items like colanders or sieves can generate multiple projections simultaneously, as each hole functions as a separate pinhole, creating an array of small solar images on a nearby surface. Commercial or DIY cereal box viewers, often promoted by educational resources, enclose the pinhole and screen within the box for portable, enclosed viewing. For optimal setup, position the projection surface 1 to 2 meters from the pinhole to achieve a viewable image size while minimizing distortion. The projected image scales linearly with the focal length—the distance from the pinhole to the surface—with a typical example yielding a 1 cm diameter image at a 10 cm distance. Users should stand with their back to the Sun, ensuring the pinhole aligns to cast the projection in shade for best contrast. These viewers offer significant advantages, including zero risk to the eyes from direct sunlight and the ability to accommodate group observations, particularly for children or crowds during events like eclipses. However, limitations include reduced image sharpness due to diffraction effects from very small apertures and geometric blurring from larger ones, as well as potential distortion from atmospheric turbulence.Specialized Filters and Devices
Specialized filters and devices for solar viewing extend beyond basic eyewear to enable detailed observation of specific solar phenomena, often integrated with telescopes or electronic systems for professional and amateur use. Hydrogen-alpha (H-alpha) filters, typically mounted on solar telescopes, isolate the 656.3 nm wavelength to reveal dynamic features such as prominences—vast plasma loops extending from the Sun's surface—that are invisible in white light due to overwhelming photospheric glare.[20][21] These filters require narrow bandpass designs, often 0.5–0.7 angstroms, to achieve sufficient contrast for prominences and filaments. White-light filters, in contrast, permit broadband visible light transmission to highlight sunspots and faculae on the photosphere, providing a foundational view of solar surface activity.[22][23] Designs for these filters prioritize safety and optical quality, with materials like Baader AstroSolar film or Thousand Oaks Optical glass achieving an optical density (OD) of at least 5 to block over 99.999% of incoming solar radiation, preventing thermal damage to optics or observers.[24][25] Baader film, a metallized polyester, offers high planarity for distortion-free imaging when cell-mounted on telescope apertures up to 300 mm, while Thousand Oaks glass variants provide durability against environmental exposure. Electronic devices, such as solar imagers, employ charge-coupled device (CCD) sensors behind protective filters to capture and project safe, real-time images, often outputting to monitors or computers for enhanced analysis without direct ocular exposure.[26] In applications, these tools support amateur astronomy clubs by facilitating group observations of solar dynamics, such as evolving prominences during outreach events, and enable research into fine-scale features like solar granules—convection cells approximately 1,000 km in diameter visible in high-resolution white-light setups.[27][28] Integration with smartphones via apps like Solar Snap allows filtered phone cameras to record solar events, combining portability with guided exposure controls for citizen science contributions.[29] Despite their capabilities, these specialized devices carry limitations, including costs starting above $50 for basic white-light filters and exceeding $500 for H-alpha systems, alongside the need for precise alignment to ensure even illumination and ongoing maintenance to prevent filter overheating from concentrated solar energy.[30][31]Optical Principles
Light Filtering Mechanisms
Solar viewers attenuate the Sun's intense radiation through mechanisms that control the absorption, reflection, and transmission of light across specific wavelengths, ensuring only safe levels reach the observer's eyes. Absorption occurs when filter materials convert incident photons into heat, reflection bounces light away from the filter surface, and transmission allows a minimal fraction of light to pass through, with the balance of these processes governed by the material's optical properties.[32][33] The effectiveness of these mechanisms is quantified by optical density (OD), defined aswhere is the transmittance, the ratio of transmitted to incident light intensity. For safe direct solar observation, filters must achieve OD in the visible spectrum (400–700 nm), corresponding to or transmittance of at most 0.001%, which blocks 99.999% of visible light and prevents retinal overload.[34][35] Filters vary by type to suit different observational needs: neutral density filters provide broadband attenuation across the visible spectrum for general white-light viewing, while selective filters, such as H-alpha types, transmit a narrow band centered at 656.3 nm—the wavelength of hydrogen-alpha emission—to reveal red prominences and chromospheric features against a darker background. Materials commonly used include black polymer films embedded with carbon particles for primary absorption, yielding a yellow-orange solar image, and coated glass substrates that combine reflection from metallic layers (e.g., aluminum) with absorption for enhanced durability.[35][36][32] To address specific hazards, solar filters rigorously block ultraviolet (UV) wavelengths below 400 nm and infrared (IR) above 700 nm; UV blocking mitigates photochemical damage, including the blue-light hazard that triggers damaging chemical reactions in retinal cells, while IR blocking prevents thermal injury from heat buildup in eye tissues. Compliance with standards like ISO 12312-2 ensures UV transmittance below 0.0032% (e.g., 0.00000015%–0.0000026% for UVB at 280–315 nm) and IR transmittance around 0.01%–1.29% (700–2000 nm), far exceeding visible light attenuation.[37][35] Performance metrics for direct viewers emphasize low transmission rates, typically 0.00004%–0.0012% luminous transmittance to balance visibility and safety, with darker filters (e.g., OD >5.9) preferred for comfort during prolonged observation. Filter integrity can degrade over time due to physical damage like scratching, which scatters light and reduces OD, or delamination in polymer films, creating pinholes that allow unfiltered light to bypass attenuation and pose risks. Regular inspection for defects larger than 0.2 mm or clustered imperfections is essential to maintain efficacy.[35][37] These mechanisms underpin direct optical viewers and specialized devices by reducing solar intensity without distorting essential image details.[32]