Infrared heater

An infrared heater or heat lamp is a heating appliance containing a high-temperature emitter that transfers energy to a cooler object through electromagnetic radiation. Depending on the temperature of the emitter, the wavelength of the peak of the infrared radiation ranges from 750 nm to 1 mm. No contact or medium between the emitter and cool object is needed for the energy transfer. Infrared heaters can be operated in vacuum or atmosphere.

One classification of infrared heaters is by the wavelength bands of infrared emission.

German-British astronomer Sir William Herschel is credited with the discovery of infrared in 1800. He made an instrument called a spectrometer to measure the magnitude of radiant power at different wavelengths. This instrument was made from three pieces. The first was a prism to catch the sunlight and direct and disperse the colors down onto a table, the second was a small panel of cardboard with a slit wide enough for only a single color to pass through it and finally, three mercury-in-glass thermometers. Through his experiment Herschel found that red light had the highest degree of temperature change in the light spectrum, however, infrared heating was not commonly used until World War II. During World War II infrared heating became more widely used and recognized. The main applications were in the metal finishing fields, particularly in the curing and drying of paints and lacquers on military equipment. Banks of lamp bulbs were used very successfully; though by today's standards the power intensities were very low, the technique offered much faster drying times than the fuel convection ovens of the time. After World War II the adoption of infrared heating techniques continued but on a much slower basis. In the mid 1950s the motor vehicle industry began to show interest in the capabilities of infrared for paint curing and a number of production line infrared tunnels came into use.

The most common filament material used for electrical infrared heaters is tungsten wire, which is coiled to provide more surface area. Low temperature alternatives for tungsten are carbon, or alloys of iron, chromium, and aluminum (trademark and brand name Kanthal). While carbon filaments are more fickle to produce, they heat up much more quickly than a comparable medium-wave heater based on a FeCrAl filament.

When light is undesirable or not necessary in a heater, ceramic infrared radiant heaters are the preferred choice. Containing 8 meters (26 ft) of coiled alloy resistance wire, they emit a uniform heat across the entire surface of the heater and the ceramic is 90% absorbent of the radiation.^{[clarification needed]} As absorption and emission are based on the same physical causes in each body, ceramic is ideally suited as a material for infrared heaters.^{[citation needed]}

Industrial infrared heaters sometimes use a gold coating on the quartz tube that reflects the infrared radiation and directs it towards the product to be heated. Consequently, the infrared radiation impinging on the product is virtually doubled. Gold is used because of its oxidation resistance and very high infrared reflectivity of approximately 95%.

Infrared heaters are commonly used in infrared modules (or emitter banks) combining several heaters to achieve larger heated areas.

Infrared heaters are usually classified by the wavelength they emit: