Question on UVA and NUV wavelengths

[PhotonWrangler]

A thought occurred to me (I try not to let this happen too often - it gives me terrible headaches).

Anyway, when I think about how an NUV LED looks to my eyes, that purple glow, it makes me wonder where the cutoff wavelength is for eye sensitivity to NUV. When you consider that said UV causes the corneas to fluoresce, thus creating an illusion of increased visibility at said wavelength, where's the cutoff?

I know that it's not really a cutoff wavelength per se, but a gradual rolloff in sensitivity, but where does a human eye fall off the UV end of the scale? Where's the 3db attenuation point? 390nm? 365nm? Shorter?

[Zelandeth]

The real headscratcher here is how much visible light is also being produced by the source. UV LED's I can't really comment on, as I've only seen one.

Fluorescent blacklights however I can comment on.

The problem with them however, is that all the "Light" you observe from them, is not necessarily in the UV area, there IS an emmision band in the deep violet (probably enough to cause fluorescence of the eye's cornia, given that this effect can be observed with some of the deeper blue LED's as well) as well as the primary 352nM emission - which is invisible to the human eye.

As I recall (though I can't find the document I'm looking for to save my life), anything below 400nM is considered to be invisible - DON'T quote me on that though!

[Ken_McE]

Don't know if I can answer your question exactly, but here's some background:

400 nanometers is the traditional cutoff between violet and ultraviolet. The shortwavelength (blue) cells in your eye would respond to shorter wavelengths, but your eye is designed to keep them out of there. There is a yellowish layer in the front of the eye that serves mostly to block UV.

UV radiation is harmful to living tissues. Short lived species such as deer and bees can and do see into the ultraviolet. They will age and die before the UV does them any real harm. Long lived species like us have to keep UV out of the eye or we will go blind from it.

I have seen the suggestion that crepuscular animals (creatures that are active around dawn and dusk, and avoid full night and full daylight) may be able to use UV so as to see clearly where you and I would just see dark blurs. I have not researched this theory properly.

People who have cataract surgery lose the UV filter and after that they have to wear UV blocking sunglasses when they go outside. I am fuzzy about the *exact* point where the visual response starts. There is some variation between individuals. I don't know if anyone has studied the boundry area closely. You would think someone must have...