The Whitest Whites

By Anupum Pant

Florescence is a physical phenomena in which light (electromagnetic radiation) is absorbed by a substance with certain properties and is instantly emitted back in a different wavelength. Most times the absorbed light of a certain wavelength is emitted back by the substance with a greater wavelength. This leads to one interesting phenomenon in which the smaller wavelength UV radiation (which is invisible to the human eye) gets converted to a visible light by the substance. Applications of this particular phenomenon are numerous, in the modern world.

The white fluorescent lamps we see lighting up most of the things these days (getting quickly replaced by white LEDs) contain a fluorescent substance which does the same thing. The vapour inside these lamps gets excited and produces a UV light, had the fluorescent phosphor coating not been there in these lamps, you wouldn’t have seen any bright light come out of them.

But the most interesting application that I had not known until today is them being used in optical brighteners or fluorescent whitening agents in detergents that are commercially available to help you make your whites appear more white than they actually are. When you treat your clothes with these brighteners, the clothes now have this substance clinging to it which can absorb the UV in sunlight and emit a blue light. So, the yellow from your whites mixes with this blue and you see your clothes are more white in the sun outside.

If people in the military decide to wear whites washed with detergents like these, they’d be in big trouble. It would make them glow in nightvision goggles.

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