Question: What causes some objects to glow under a black light?
Black lights give off Ultraviolet A light, which is a type of high-energy invisible light (radiation). Photons are packets of light energy. UV light photons have a higher energy than do the photons for visible light.
Materials that glow under a black light contain a type of chemical called a phosphor. When phosphors absorb UV photons, some of the electrons in the atoms making up the phosphor become energized or excited. This means that the electrons move further way from the nucleus.
But, these energized electrons release visible light photons and return to their normal position, called ground state. The released photons have a lower energy than do UV photons.
The glow from a phosphor is an example of photoluminescence. WOW! That is a big word, but it is actually easy and certainly fun to experiment with. Let’s take the word apart:
photo is a prefix for light
luminescence is any cold light–light from something that is not hot.
OK, if we put the word parts back together we have a cold light produced by some light source.
Phosphors only glows during the time they are exposed to black light (UVA). This type of luminescence is called fluorescence.
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