Ultraviolet (UV) light is a type of electromagnetic radiation that is invisible to the human eye, with wavelengths ranging from 180 to 400 nanometers. It is used in a variety of applications, from scientific instruments to black lights and fluorescent dyes. But what materials let UV light through?UV grade fused silica is a transparent material for wavelengths up to 200 nm. The cheaper, standard-grade fused silica is transparent for wavelengths below 260 nm.
The artificial diamond is transparent up to 230 nm. Borate crystals such as BBO and LBO also have relatively good UV transparency. UV detectors are sensitive to most fires, including hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. Arc welding, electric arcs, X-rays used in non-destructive metal testing equipment (although this is very unlikely), and radioactive materials can produce levels that activate a UV detection system. The presence of gases and vapors that absorb UV rays attenuates the UV radiation of the fire and negatively affects the detector's ability to detect flames.
Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect. A blazing hydrogen flame, for example, radiates strongly in the 185 to 260 nanometer range and only very weakly in the IR region, while a charcoal fire emits very weakly in the UV band but very strongly at IR wavelengths; therefore, a fire detector that works with UV and IR detectors is more reliable than one with a UV detector alone. As a result of the growing need for sanitation measures related to COVID-19, procurement activity has increased, including the search for suitable materials, such as highly temperature-resistant and UV-transparent fused silica glass, for ultraviolet light applications. These lamps emit ultraviolet light with two peaks in the UV‑C band, at 253.7 nm and 185 nm, due to the mercury contained in the lamp, in addition to part of the visible light. In addition, the UV transmittance of glass samples gradually decreased as the Al2O3 content increased, and the UV transmittance of glass samples first increased and then decreased as the B2O3 content increased. Black lights are used in applications where extraneous visible light must be minimized; mainly to observe fluorescence, the colored glow that many substances emit when exposed to ultraviolet light. Many pigments and dyes absorb UV rays and change color, so paints and fabrics may need additional protection against both sunlight and fluorescent lamps, two common sources of UV radiation.
Specialized UV gas discharge lamps containing different gases produce UV radiation in specific spectral lines for scientific purposes. Black-light fluorescent lamps work in a similar way to other fluorescent lamps, but they use a phosphor on the inner surface of the tube that emits UV-A radiation instead of visible light. In 1999, Kimlin and Parisi studied solar UV radiation transmitted through normal and tinted car windows and discovered that glass tint provided significant protection against UV radiation. Many everyday materials influence the UV radiation that humans receive; for example, those used in construction and outside buildings, such as plastics and glass, can reduce UV exposure for people exposed to solar radiation. Some scientific instruments use halogen lamps with molten quartz envelopes as low-cost UV light sources in the range close to UV rays, 400 to 300 nm.
Because the ozone layer prevents many UV frequencies from reaching telescopes located on the Earth's surface, most UV observations are made from space. UV fluorescent dyes that shine in primary colors are used in paints, papers and textiles, either to enhance color in daylight or to provide special effects when illuminated with UV lamps. Colorless fluorescent dyes, which emit blue light under UV rays, are added as optical brighteners to paper and fabrics. Incandescent black lights are also produced using a filter coating on the envelope of an incandescent bulb that absorbs visible light (see the next section).