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1 Tsuga  Sun, Mar 23, 2014 1:25:57pm

Really interesting and important, but the science is rather simplistic. Digging through the links provides a better understanding: Conservation Biology and Proceedings of the Royal Society.

A little background is helpful. UV is not a single entity that you either see or don’t see. Rather, it’s a very broad range of wavelengths (~5 octaves of frequencies, vs. <1 octave for visible light), ranging from 10 nanometers (nm) to 400 nm. Visible light is classified as 400 nm to 700 nm.

Other creatures have varied abilities to see UV. Many insects, reptiles, and birds have excellent UV vision and can see down to around 300 nm, because they have retinal cells dedicated to this range. There’s not much point in seeing below around 300 nm since almost all UV wavelengths shorter than this and coming from the sun are filtered out by the ozone layer (though lightning will emit UV well below 300 nm). Below 200 nm, air itself is opaque to UV.

The frequency response of the human visual system doesn’t suddenly cut off at a single frequency, but rather fades out gradually around the far end of what we call violet. Thus, the ‘boundary’ between visible light and UV has been selected to be 400 nm, beyond which our visual system normally has minimal and then no response to light. This means that many people can see a very little bit of the UV down to 380 nm or so, but our visual response in this range is so slight that it’s not a significant part of our vision under any but the most unusual circumstances.

However, part of the reason for this is the ocular lens filtering out UV below this range. People who have had a lens removed commonly can see more UV, some of it down to around 350nm. For these people, UV actually stimulates all three types of cone cells to produce a bluish-white addition to their vision that’s evident when UV is a part of the spectrum they’re observing. This is apparently what is also happening to those mammal species having eyes capable of transmitting enough UV all the way to the retina, as described in the links.

2 FemNaziBitch  Sun, Mar 23, 2014 1:31:03pm

Why do birds sit on the wires and squirrels scamper along them?

3 Tsuga  Sun, Mar 23, 2014 1:32:46pm

re: #2 FemNaziBitch

Because those are low-power lines that don’t produce the same effects.

4 Charles Johnson  Sun, Mar 23, 2014 1:35:40pm

re: #1 Tsuga

The problem with your post was the < symbol in your text, because that’s the opening character of HTML tags and our code sanitizing routine causes everything after it to be stripped out.

You can enter that character by using the entity instead, for example: &lt;

5 Tsuga  Sun, Mar 23, 2014 1:46:27pm

Thanks, Charles. Looks like you fixed the format for me.

6 Charles Johnson  Sun, Mar 23, 2014 2:32:35pm

re: #5 Tsuga

A little background is helpful. UV is not a single entity that you either see or don’t see. Rather, it’s a very broad range of wavelengths (~5 octaves of frequencies, vs. <1 octave for visible light), ranging from 10 nanometers (nm) to 400 nm. Visible light is classified as 400 nm to 700 nm.

Testing…

7 Tsuga  Sun, Mar 23, 2014 2:52:19pm

OK, now I see the problematical character I used originally. After your response, I’d quickly assumed (without thinking about it) that I messed up the formatting for the links somehow , when that was not it at all. Thanks for the education, and sorry for my cluelessness.

8 sauceruney  Sun, Mar 23, 2014 4:01:29pm

So there’s a possibility of using UV beacons on vehicles to help minimize collisions with deer?

9 Charles Johnson  Sun, Mar 23, 2014 5:35:30pm

re: #7 Tsuga

OK, now I see the problematical character I used originally. After your response, I’d quickly assumed (without thinking about it) that I messed up the formatting for the links somehow , when that was not it at all. Thanks for the education, and sorry for my cluelessness.

This inspired me to write a regular expression that makes the problem a thing of the past. You can now use left angle brackets to your heart’s content, no need to use the character entity.


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