What Colors Glow in Black Lights?

Written by katherine harder
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What Colors Glow in Black Lights?
Blacklight bulbs are actually ultraviolet light bulbs. (rallas image by Carlos-bcn from Fotolia.com)

Fluorescent substances like to absorb ultraviolet light because it has a short wavelength. When ultraviolet light, or blacklight, shines on an object or surface that contains fluorescence, the ultraviolet light is absorbed and re-emitted in a longer wavelength, becoming visible. Generally any colour with an amount of fluorescence or phosphorescence will react with a blacklight, although reds are very low on the spectrum and most don't react well to blacklight even when treated chemically to increase ultraviolet visibility; an exception to this rule is blood, which like other common bodily fluids, contains fluorescence and glows brightly under blacklight.

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When you think of blacklight reactive colours, your mind probably immediately thinks of white. Actually, the white itself isn't blacklight reactive, but many white objects are treated with fluorescent compounds which are reactive. For example, white paper is treated chemically with fluorescent compounds to increase brightness. Paper before 1950 wasn't treated with these compounds and therefore doesn't glow under blacklight. In the same vein, washing powder contains fluorescence to increase whiteness, which contributes to the blacklight reactivity of white clothes; fluorescence in toothpaste make teeth look whiter in normal light and extra bright under ultraviolet light.


Many clear objects react to blacklight, including diamonds, cat urine and "invisible" blacklight-reactive paint. Club soda gets its bitter taste from the quinine found in the beverage; quinine is a fluorescent compound and appears blue under blacklight. Petroleum jelly is another clear substance that contains phosphors and therefore absorbs and re-emits ultraviolet light.

Fluorescent Colors

"Hot" colours such as hot pink, hot orange and hot yellow contain phosphors to increase the brightness of their hues. These colours glow very brightly under blacklight due to the high amount of phosphorescent compounds used to create them. Paints treated with fluorescent compounds to become blacklight reactive also glow under ultraviolet light; these paints come in virtually every hue.

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