Why Does Urine Glow Under a Black Light?

Element in Urine That Glows

Urine glows when exposed to black or ultraviolet light.
Urine glows when exposed to black or ultraviolet light. WIN-Initiative / Getty Images

You can use a black light to detect body fluids. It's actually a good way to look for pet urine or make sure a bathroom or hotel room is really clean. Cat urine, in particular, glows very brightly under ultraviolet light. Urine glows under a black light primarily because it contains the element phosphorus. Phosphorus glows yellowish green in the presence of oxygen, with or without black light, but the light imparts additional energy that make the chemiluminescence easier to see.

Urine also contains broken down blood proteins that glow under a black light.

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Helmenstine, Anne Marie, Ph.D. "Why Does Urine Glow Under a Black Light?" ThoughtCo, Sep. 27, 2017, thoughtco.com/why-urine-glows-under-black-light-609449. Helmenstine, Anne Marie, Ph.D. (2017, September 27). Why Does Urine Glow Under a Black Light? Retrieved from https://www.thoughtco.com/why-urine-glows-under-black-light-609449 Helmenstine, Anne Marie, Ph.D. "Why Does Urine Glow Under a Black Light?" ThoughtCo. https://www.thoughtco.com/why-urine-glows-under-black-light-609449 (accessed May 22, 2018).