How Do Black Lights Work?

Fluorescent Light with Phosphor

Black lights are a kind of fluorescent light with a special coating of phosphor, functioning as a ubiquitous accessories in college dorm rooms. Phosphors fluoresce (give off light) when hit by radiation. The black glass in a black light blocks normal visible light so the only light hitting the phosphor coating is in the ultraviolet spectrum.

Ultraviolet Light

Ultraviolet light is electromagnetic radiation just like visible light but it is slightly more energetic. Undetectable by the human eye, when UV light hits certain materials, called phosphors, it causes them to glow. Phosphors change the energy from the UV radiation to light we can see (visible light).

Glowing Teeth and Other Stuff

Many things in nature contain phosphors, like your teeth and fingernails. That is why they glow underneath a black light. Special paints, fabrics and fluorescent pens and markers also contain phosphors. This is why your white T-shirt glows under a black light. Black light products at clubs use paint and materials with a high phosphor content so they glow earlier under the black lights.