A black light produces fluorescent lighting with ultraviolet rays. When people see things glow in the dark, black lights are what create that effect. The light has a longer wavelength than X-ray light and is shorter than the light that people normally see. Things normally invisible to the eye become visible with a soft, violet fluorescent glow.
Black lights are used to sterilize equipment in hospitals and to inspect operating rooms for germs before surgery. This is a quicker and less tedious process then the autoclave sterilization method. The equipment should be cleaned and wiped dry before sterilization, because ultraviolet rays cannot penetrate through dust or dirt that may be blocking the object's surface. Black lights also are used to cure dental materials, making them ready for use on patients within seconds.
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Home and Business
The food industry uses black lights when packing products. The rays alert companies to invisible germs that can produce bacteria and spoil food. Theme parks sometimes stamp a person's hand with an invisible fluorescent mark upon entrance to the park. If the guest leaves the park during the day, park employees use a black light to identify the guest's mark upon re-entry. Black lights also can show hidden urine stains from pets living inside a home. The urine will glow under the rays from the black light, resulting in easier cleanup and helping to prevent odors.
Science and Insects
Scorpions have fluorescent chemicals inside their bodies, and ultraviolet rays will cause the creature to glow. Scientist use black lights to locate scorpions for research. In addition, campers can use black lights in "bug zappers" that keep the area around their tents and sleeping quarters free from stinging or biting pests such as mosquitoes. The black lights attract the insects, zapping and killing them as they land on the bulb.
Banks and retail stores use black lights to check the authenticity of large bills of currency. The ultraviolet rays detect markings on the bills that are invisible to the naked eye. When paying a ransom for a kidnapping, officials may mark the bills with a fluorescent ink pen for later identification. Driver's licenses in many states also have invisible symbols on them that are extremely difficult to duplicate, making it easier for a police officer to use black light to determine if a license is authentic.