You Can See UltraViolet

By Anupum Pant

Last semester I took a course, some part of which dealt with the optical properties of materials. There I learnt a lot about how saying something is transparent and something else is opaque is meaningless unless you mention the particular wavelength you are talking about.

So, take your average glass for instance. It’s fairly transparent in the visible spectrum. So you see it as transparent, and nothing more. If you go ahead and increase the energy of light, thereby decreasing the wavelength, at some point the glass will become opaque. Similarly, a typical metal would look opaque to you because it is opaque in the visible spectrum. However, as you increase the energy of em radiation and move into the ultraviolet region, metals start becoming transparent.

The lens of your eye works like a typical glass. It’s transparent in the visible region, but becomes opaque as the energy increases and goes to the UV range. That’s the reason UV doesn’t get inside and you don’t see in UV. Had there not been a lens there,  your retina would have received UV and you would have been able to see some part of UV (from 400-300 nm wavelength).

This actually happens to people who, due to complications in the eye, like cataract and other diseases, have to get their natural lens out. This absence of lens is called Aphakia. These people start seeing a part of UV, usually from 400 to 300 nm and see the normal white light as a bluish white or a violet white light. That is because, due to the UV being detected by the blue cones in their retina, their blue cones get excited more than the others.

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