作者：紫外光源事业部时间：2020-02-18 20:40浏览140 次
Ultraviolet (UV) radiation occupies the portion of electromagnetic spectrum from 100 to 400 nanometers (nm). The UV spectrum consists of three regions:
UV-A (315–400 nm)
UV-B (280–315 nm)
UV-C (100–280 nm)
For most people, the main source of UV exposure is the sun. Exposure from the sun is typically limited to the UV-A region, since the earth’s atmosphere protects us from the more harmful UV-C and UV-B regions. Only artificial light sources emit radiant energy within the UV-C band.
UV generating devices may contain one or a combination of a couple or more artificial light sources (UV lamps) in order to achieve the desired light quality. Below are listed some of the most used types of UV generating lamps.
Xenon arc lamp
A xenon (Xe) arc lamp is a specialized type of gas-discharge lamp that produces light by passing electricity through ionized xenon gas at high pressure. The lamp generates a bright white light that closely mimics natural sunlight. Xenon arc lamps are used in movie theater projectors and searchlights, as well as in industry and research to simulate sunlight.
There are three main types of xenon arc lamps: continuous-output short-arc, continuous-output long-arc, and flash.
Xe short-arc lamps come in two distinct varieties: pure xenon, which contains only xenon gas, and xenon-mercury, which contains xenon gas and a small amount of mercury metal. Xenon-mercury short-arc lamps have a bluish white spectrum and extremely high UV output. These lamps are used primarily for UV curing applications, sterilizing objects, and generating ozone.
Xe long-arc lamps are structurally similar to short-arc lamps except that the arc-containing portion of the glass tube is greatly elongated. When mounted within an elliptical reflector, these lamps are frequently used to simulate sunlight. Typical uses include solar cell testing, solar simulation for age testing of materials, rapid thermal processing, and material inspection.
All xenon short-arc lamps generate substantial ultraviolet radiation. Xenon has strong spectral lines in the UV bands, and these readily pass through the fused quartz lamp envelope. The UV radiation released by a short-arc lamp can cause a secondary problem of ozone generation.
Equipment that uses short-arc lamps as the light source must keep the UV radiation contained and prevent ozone buildup.
Many lamps have a shortwave UV-blocking coating on the envelope and are sold as “ozonefree” lamps for solar simulator applications. Some lamps have envelopes made out of ultra-pure synthetic fused silica (such as “Suprasil”), which allows them to emit useful light into the vacuum UV region. These lamps are normally operated in a pure nitrogen atmosphere.
Xe flash lamps typically provide 80 flashes per second and are used in movie theater projectors and searchlights, as well as in industry and research to simulate sunlight. Other applications include air pollution analysis, biochemical analysis, blood or urine analysis, color sensing, factory automation, gas analysis, precision photometry, semiconductor inspection, shape inspection, and spectrophotometry.
Metal halide arc lamp
A metal halide lamp is an electric lamp that produces light via an electric arc through a gaseous mixture of vaporized mercury and metal halides (compounds of metals with bromine or iodine). The most common metal halide compound used is sodium iodide. Once the arc tube reaches its running temperature, the sodium dissociates from the iodine, which adds orange and red to the lamp’s spectrum from the sodium D line as the metal ionizes. As a result, metal halide lamps produce an intense white light and have high luminous efficacy at approximately 75–100 lumens per watt, which is about twice that of mercury vapor lights and three to five times that of incandescent lights and. Lamp life is 6,000 to 15,000 hours. Primarily developed for use in film and television lighting, which requires a high temporal stability and daylight color match, metal halide lamps are used for wide-area overhead lighting for commercial, industrial, and public spaces, such as parking lots, sports arenas, factories, and retail stores, but also for residential security lighting. Most types are fitted with an outer glass bulb to protect the inner components and prevent heat loss. The outer bulb can also be used to block some or all of the UV light generated by the mercury vapor discharge. The metal halide lamp requires a warm-up period of as long as five minutes (depending on the lamp type). While it warms up, the lamp exhibits different colors as the various metal halides vaporize in the arc chamber.
Mercury vapor lamp
A mercury vapor lamp is a gas-discharge lamp that produces light via an electric arc through vaporized mercury. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb.
In low-pressure mercury vapor lamps, only the lines at 184 and 253 nanometers (nm) are present. Only the light at 253 nm is usable. Synthetic quartz can be used in the manufacturing to keep the 184 nm light from being absorbed. In mediumpressure mercury vapor lamps, the lines from 200–600 nm are present. The lamps can be constructed to emit primarily in the UV-A (around 400 nm) or UV-C around 250 nm). High-pressure mercury vapor lamps are those lamp commonly used for general lighting purposes. They emit primarily in the blue and green.
Some mercury vapor lamps (including metal halide lamps) must contain a feature that prevents ultraviolet radiation from escaping. Even with these methods, some UV radiation can still pass through the outer bulb of the lamp. This accelerates the aging process of some plastics, leaving them significantly discolored after only a few years’ service. Polycarbonate suffers particularly from this problem, and it is not uncommon to see fairly new polycarbonate surfaces positioned near the lamp that have turned a dull yellowish brown color after only a short time.