A Woods lamp is a small ultraviolet lamp (also called a UV light or a black light) with an output of 253.7 nm. The general shape is a rectangular plastic box with 2-4 ultraviolet bulbs and usually a magnifying window in the center. The power cord comes out the base of the handle to stay out of the way during use. Some models also have white light bulbs for standard illumination.
Woods lamps have a wide number of uses centered around one specific function: detecting items which fluoresce. Since many items do, Woods lamps are used in such wide-ranging fields as police work, veterinary care, and dermatology. Woods lamps currently sell for around $170.00 on Amazon.com.
In police work and other such investigations, Woods lamps can be used to find semen stains and traces of urine, both of which glow under UV light. For this reason, Woods lamps are found in rape kits and play a role in investigating sexual assault. Specifically, the enzyme known as alkaline phosphatase is the part of semen that fluoresces.
In medical work, Woods lamps are used to diagnose certain fungus and parasites. Scabies and about half of all ringworm species, for example, glow under UV light. Another medical application is the detection of scratches in the cornea of the eye. A fluorescent dye is applied to the eyeball, which collects in any scratches that may be there. The Woods lamp then illuminates the scratches.
I was, unfortunately, unable to track down the origin of the name "Woods lamp." If anyone could help me with this, I would appreciate it.
Thanks to jasonm who tells me that apartment managers also use a Woods lamp to check the carpet for urine stains after a pet owner moves out.