Black lights emit a very dim, purplish light that sets a great mood for a party. Halloween parties or haunted houses often use black lights, but these lights can also help to create a fun, neon, glowing atmosphere for any occasion.
A black light emits ultraviolet rays that are very bright, but humans can't see them. Fluorescent objects absorb the ultraviolet light rays given off by a black light so that human eyes can see it.
Neon-colored fluorescent paper, clothing or highlighter ink glows under the black light. Special black-light fluorescent paint and markers are sold at most craft stores. The color will appear about the same as in normal light but much brighter.
Some other common objects glow under a black light. White t-shirts typically glow bright under a black light. Typically, this is due to the bluing agents in laundry detergents that are phosphors reacting to the ultraviolet light rays from the black light. The new $20, $50 and $100 U.S. bills (those made after 2003) also have a security thread through it that reacts to black lights.
A phosphorescent glow can last a few minutes even after the black light is turned off. Many glow-in-the-dark products will also work in black light. Petroleum jelly looks nearly invisible in normal light but glows brightly in black light.
To put black light on some parts of a room and not others, try a shield that blocks the UV rays. Quartz glass and automotive glass work well. Special lighting-filter gel will stop the ultraviolet rays but allow normal light through.