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Comment by shiandow | Hacker News Reader

More to the point >400nm is visible light, this puts 148nm well within the ultraviolet range. Though it's not too far removed from the visible spectrum, wouldn't surprise me if some animals could see it.

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148 doesn't feel too far removed from the visible spectrum, but it's in the wrong direction for animals to make use of it. I'm no biologist, but I'd be shocked if there were any animals that had adapted sensitivity to a type of radiation that they are never exposed to in nature. The sun doesn't really emit much UV-C light:

https://en.wikipedia.org/wiki/Solar_irradiance#Absorption_an...

and the light that is emitted is absorbed by the atmosphere:

https://en.wikipedia.org/wiki/Ultraviolet#Solar_ultraviolet

It's useful to be able to see a little UV-A, perhaps, and very useful for predators to see 'heat' into the IR range, but if your eyes were sensitive to 148nm, the world would be pretty dark.

Maybe after a few million years, in the grinding dust in the back of my shop, something will evolve that has a symbiotic relationship to arc welders...

Ah, yeah makes sense that animals couldn't see it if it's not really part of sunlight. I was thinking it was not physically impossible, but it would be remarkably pointless if the light is simply not there.

I don't see how it could get into an organism if it's absorbed by air and water.

Also, even if there was some advantage to doing so, i'm not sure how animals could see a wavelength that short. They would need a photoreceptor protein which can absorb photons of that wavelength and turn them into some sort of chemical change which can trigger a signalling cascade. That protein would have to have a pair of molecular orbitals which are h * 148 nm apart. What can give you that?

The ethene double bond absorbs at ~165 nm, a benzene ring at ~180 nm, and building things out of those tends to increase the wavelength, not decrease it. 148 nm is single bond territory - could you have a chromophore which uses photons of the right wavelength to break a bond, and then somehow react to the presence of free radicals?!

A long time ago I saw some UV photos of flowers, compared to visible and IR. There were some distinct features. That suggests some insects could see them, but of course it's just speculation.

That would be UV-A, I believe. Not UV-C.

It's not speculation. Bee eyes have receptors for green, blue, and UV-A light, for example. But as BenjiWiebe mentioned, that's not the same as being sensitive to UV-C.

I'm sure there would be some value in seeing others parts of UV. Some minerals fluoresce from one type of UV light but not another, so they'd be dark in the bands that cause them to fluoresce. Mantis shrimp can apparently see into UV-B, but I'm not aware of anything living that can see UV-C.

Many animals do have more UV extension than you might initially assume useful: due to scattering following the inverse fourth power of wavelength the sky is lit in the UV a long time before sunrise.

Presumably wouldn't apply anywhere near as far as 148nm since as you note that light doesn't make it to earth.

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