Ultraviolet bulbs produce light that falls primarily in the ultraviolet—also known as UV—spectrum. The bulbs are usually designed to create light in one of many specific UV wavelength bands. Ultraviolet bulbs are often coated with a phosphor, which blocks most light outside of the desired frequency range. Laboratory sterilizers, as well as air and water purifiers, can use UV bulbs to perform their treatments. Ultraviolet lamps are also used in electronics manufacturing and in the curing of adhesives and other coatings.
The UV spectrum ranges from long-wave ultraviolet around 400 nanometers (nm) down to extreme ultraviolet near 10 nm. The energy of these wavelengths rises from about 3 electron volts (eV) to 124 eV as the wavelength decreases. Ultraviolet bulbs are manufactured in different ways depending on the wavelength and use of the lamp. Some are simply uncoated fluorescent bulbs while others are doped with special types of phosphors or vapors. Ultraviolet lasers and light-emitting diodes (LEDs) exist for some applications as well.
An ultraviolet air purifier uses a photochemical process to oxidize organic materials which pass through it. This process can break down compounds with high-intensity light from a UV lamp in the 240 to 280 nm range. An ultraviolet water purifier can use ultraviolet bulbs along with filters and chemicals to sterilize drinking water. UV light is often used in large wastewater treatment plants as well. The ultraviolet light in natural sunlight can also be used to disinfect small quantities of drinking water under specific conditions.
Medical facilities and laboratories frequently use ultraviolet disinfection as one of many methods to destroy germs. Ultraviolet bulbs in the 185 to 265 nm range are particularly effective at preventing their deoxyribonucleic acid (DNA) replication. UV lamps are often used in food production as well to pasteurize juices and kill some microorganisms.
Light from ultraviolet bulbs can also be used to bond materials using adhesives designed specifically for ultraviolet curing. Specially-prepared coatings can be cured with UV lamps as well, including those on paper, flooring and dental fillings. Even inks used in offset printing can be rapidly cured with high-intensity light from high-pressure bulbs.
The electronics industry utilizes ultraviolet bulbs for photolithography. This process is used in the manufacture of printed circuit boards to chemically draw electrical connections. A similar process is used in the creation of semiconductors, including integrated circuits. In the 1980s and 1990s, low-power ultraviolet light was also used to erase some types of non-volatile memories.