If you're trying to read hidden messages, detect counterfeit cash, look for traces of blood or just trying to find out where your cat pees, a homemade black light is an indispensable tool. Black lights make objects appear to glow if the objects contain chemicals called phosphors, which convert ultraviolet (UV) light into visible white light as a form of radiation. The science behind black lights may be complicated, but the process of creating your own homemade black light is not.
Place the light socket against the bottom of the cup, and trace the circumference of the socket with a pencil. Cut out this section with scissors. Do the same with the plate so that both the cup and plate have holes in their centers.
Cover the entire inside of the cup, with the exception of the hole you cut, with aluminum foil to create a reflective surface that will serve to magnify and direct the light.
Place the plate and cup together (both right side up) so that the holes you cut out line up with one another, and glue into place.
Insert the socket into the cup from behind the plate so that the corded end comes out from behind the plate and the open side of the socket is in the cup. The further down in the cup you place the socket, the more magnification and direction the light will yield.
Screw an ultraviolet fluorescent light bulb, also called a black light, into the socket while the apparatus is unplugged.
Apply glue to secure the socket in place in the cup before plugging in, if desired.
Plug in and turn on your homemade black light with the light pointed away from your eyes.
Use a cup deeper than the final height of the light bulb in its socket, so that the entire apparatus can be placed face down when not in use.
Do not look directly at the light bulb while turned on because, like any other light, prolonged exposure can cause eye damage. This light is intended solely for entertainment purposes.