How do black (UV) lights work?

How do black (ultraviolet) lights work?

A black light looks dark purple, but most of the light it emits is in the ultraviolet (UV) range of the spectrum, which is invisible to the human eye.



Under a UV light, white clothes, our UV poster [link], glow in the dark and many fluorescent coloured items emit a bright glow. What they all have in common is that they contain phosphors.

A phosphor is any substance that absorbs energy and re-emits it as visible light. Under a black light, phosphors convert the UV radiation they receive into visible light.

Teeth and fingernails contain phosphors naturally, and many laundry detergents contain phosphor-based optical brighteners designed to give your white clothes that ‘whiter than white’ effect.

Aside from looking pretty in clubs, black lights have many practical uses. In particular, ink that shows up under a black light is often used on event tickets and bank notes (including British pounds, US dollars and Euros) to help detect counterfeits. 


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