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  #1  
Old 06-05-2008, 08:44 AM
Ludovic Ludovic is offline
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What does ultraviolet light look like?

Yeah yeah, another qualia question. But I'm just asking people to compare ultraviolet light to their perception of other colors, not ours, if you get my drift.

I heard that some people, due to cataract surgery, could see ultraviolet light, since we have the receptors for it in our eyes but the outer layer of our eyes block it. If so, how does this compare to deep purple (or other colors) for them?
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  #2  
Old 06-05-2008, 09:03 AM
puppygod puppygod is offline
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Apparently it smells blue.
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  #3  
Old 06-05-2008, 09:51 AM
Mijin Mijin is offline
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I think ultraviolet light looks white to those people able to see it.

That is, if ultraviolet light strikes the retina then *all* of the cones of the eye are stimulated, just as happens with white light.

I don't think you'll get an answer to your question, since as far as we know, no-one can imagine what ultraviolet light would look like, and even if they could, they would be unable to describe it.

Last edited by Mijin; 06-05-2008 at 09:53 AM..
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  #4  
Old 06-05-2008, 09:57 AM
Mangetout Mangetout is online now
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Quote:
Originally Posted by Mijin
I don't think you'll get an answer to your question, since as far as we know, no-one can imagine what ultraviolet light would look like, and even if they could, they would be unable to describe it.
And anyway, is the 'ultraviolet' I see the same as the one you see?
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Old 06-05-2008, 10:05 AM
Schnitte Schnitte is offline
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Specifying what UV light looks like involves a comparison: You pick something known which looks identical to what you are describing. Since humans can't see UV light (that's part of the definition; it's defined as the part of the spectrum between visible violet light and X-rays), it's not possible to pick another color which humans can see and say that this is what UV looks like.

OTOH, I believe (but I'm a layman at all of this) that man's inability to see ultraviolet light is due only to the lack of receptors in the eye; there's nothing in the brain which would disable it from processing information from the eye about UV light if the light were able to detect these wavelengths. So if you could connect an artificial UV detector directly to your visual cortex, you'd get an accurate impression of what ultraviolet light looks like.
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  #6  
Old 06-05-2008, 10:10 AM
Polycarp Polycarp is offline
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"Ultraviolet" is a range on the spectrum. It's kind of like asking what do red, blue, green, orange, yellow, and white light look like.

It's the lens which blocks near UV light, and there's an upper limit to what receptors would see. Those patients for whom the natural lens has been removed and an artificial lens replacing it are the ones who can see into the UV spectrum a ways. And as noted, something like a black light would throw a range of UV wavelengths that would come out "white" to them. It might be interesting to get one or more of them to volunteer and find out what their perception of monochjromatic light at several wavelengths in the near UV range turns out; I don't think this has ever been done.
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Old 06-05-2008, 10:14 AM
Mangetout Mangetout is online now
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Quote:
Originally Posted by Schnitte
OTOH, I believe (but I'm a layman at all of this) that man's inability to see ultraviolet light is due only to the lack of receptors in the eye; there's nothing in the brain which would disable it from processing information from the eye about UV light if the light were able to detect these wavelengths. So if you could connect an artificial UV detector directly to your visual cortex, you'd get an accurate impression of what ultraviolet light looks like.
I don't think so, because your visual cortex is only set up to process signals within a certain set of parameters - that is, those arising from the receptors in your eyes. Certainly you could probably stimulate it in a way so as to produce novel sensations, but there's no reason to regard that as being a 'true' representation of anything at all.
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Last edited by Mangetout; 06-05-2008 at 10:15 AM..
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  #8  
Old 06-05-2008, 10:27 AM
CalMeacham CalMeacham is offline
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If light in the near infrared gets really bright (as when you're looking at the scatter from a near IR laser) it becomes visible, but I've heard that your color response sort of "peaks out", and beyond a certain color it all looks the same. I'm willing to believe that -- I've seen laser light from beyond 700 nm, and it loks like really deep red. If there's a similar "bottoming out" at the other end of the spectrum, UV would look like deep violet.
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Old 06-05-2008, 10:39 AM
beowulff beowulff is offline
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My mother described it as deep purple, just a broader band of purple than I could see.
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  #10  
Old 06-05-2008, 11:07 AM
Mijin Mijin is offline
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The answer to "if we could see ultraviolet light, what would it look like?" rather depends on exactly in what sense we could see it.

If the the range of our eyes cones were extended such that one or more types of cones could receive partially in the ultraviolet range (and the sensitivity within other ranges were modified such that we could resolve ultraviolet light in isolation), then UV would look like our current limit of purple.

If we had another type of cone in the eye explicitly for this range then we'd probably see UV as another primary colour. And describing it as a deep purple would be like describing red as a deep green.

If we had more than one extra type of cone, we'd probably have more than one extra primary colour.

Of course beneath all this is the philosophical issue of how we can know whether we're seeing the same colour, and how we could ever even begin to describe the phenomenal experience of colour using words.
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Old 06-05-2008, 11:36 AM
Sunspace Sunspace is offline
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That guy who claimed that we have four sets of colour receptors, with the fourth one in the ultraviolet and blocked by the lens, described near-UV as 'lilac'. I presume he means, 'the same colour as a lilac blossom appears in UV'. Philosophically, this isn't anything different than describing orange things as 'orange-coloured'. But as to what it actually looks like, only those who can see it can say.

Re: Infrared... apparently IR just looks like more red. This is apparently because we don't have an additional colour sensor in the IR. Which leads to the speculation: maybe we distinguish colours based on the differences between the outputs of our colour sensors?

Last edited by Sunspace; 06-05-2008 at 11:39 AM..
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Old 06-05-2008, 11:53 AM
Sunspace Sunspace is offline
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Link to previous thread.
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  #13  
Old 06-05-2008, 06:01 PM
Napier Napier is offline
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We have receptors for it in our eyes, in the sense that our blue receptors also pick up UV. We don't have receptors specifically for UV. There'd be no value to them, if our lenses didn't pass UV.

So, UV looks like violet, to the extent you can see it.

We have four kinds of receptors, each with different spectral responses. But one of them is only used for seeing fine detail, and doesn't actually get used to distinguish colors. So, we have tricolor eyes plus some grayscale detail sensitivity that doesn't match the spectral sensitivity of any of the four colors exactly.

If you look at an ultraviolet lamp, there's typically some visible light to see, and typically some response to the ultraviolet itself. Most UV lamps aren't good at emitting JUST ultraviolet.

Also, if this counts - ultraviolet also looks hazy white. That is, your eyes can fluoresce a little bit when UV is falling on them. This creates a fog of light that you see everywhere. It is your eye responding to UV, but part of the "response" is the inadvertant fluorescense.

Last edited by Napier; 06-05-2008 at 06:02 PM..
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  #14  
Old 06-05-2008, 06:54 PM
Dr. Drake Dr. Drake is online now
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Light aside, are there ultraviolet objects in the same way there are blue and purple objects? What do those look like to humans (or, if they don't exist in nature, what would one look like to humans) --- invisible, purple, white, black?
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  #15  
Old 06-05-2008, 09:23 PM
Joey P Joey P is offline
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Quote:
Originally Posted by puppygod
Apparently it smells blue.
I heard that it tastes like a circle.
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  #16  
Old 06-05-2008, 10:28 PM
Sunspace Sunspace is offline
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Quote:
Originally Posted by Joey P
I heard that it tastes like a circle.
Metallic?
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  #17  
Old 06-05-2008, 10:39 PM
Princhester Princhester is offline
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Quote:
Originally Posted by Dr. Drake
Light aside, are there ultraviolet objects in the same way there are blue and purple objects? What do those look like to humans (or, if they don't exist in nature, what would one look like to humans) --- invisible, purple, white, black?
I assume the answer to your first question would be yes, but I don't know. Such an object would be simply one that reflected light in the ultraviolet range but absorbed all light in visible range.

Assuming a white light source (ie one that emits evenly across the visible spectrum), we perceive an object as blue because it reflects light of the frequency that we perceive as blue, and absorbs light in the rest of the visible frequency range. We see something as white if it reflects all light in the visible range equally. We see something as black if it absorbs all light in the visible range.

We would perceive something that absorbed everything in the visible range, but reflected ultraviolet as black.

Last edited by Princhester; 06-05-2008 at 10:40 PM..
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  #18  
Old 06-06-2008, 06:36 AM
Joey P Joey P is offline
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Quote:
Originally Posted by Sunspace
Metallic?
No silly, circles taste like burning.
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  #19  
Old 06-06-2008, 06:45 AM
lobotomyboy63 lobotomyboy63 is offline
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There are UV photographs, but of course they just "translate" UV light into wavelengths we can see. I have a book on ethology that shows some of flowers. UV pictures demonstrate that what are very plain-looking flowers to human look more like bullseyes to the bees, who can see UV.
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  #20  
Old 06-07-2008, 05:35 PM
Napier Napier is offline
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>are there ultraviolet objects in the same way there are blue and purple objects?

Seconding lobotomyboy63, many flowers have strong designs that are only visible in the ultraviolet, which apparently pollinating insects can see.

Many objects in general have different reflectivities in different wavelengths, which in the case of the wavelengths we can see means they have color. Of course this happens in other wavelengths too. It is a common theme in these reflectivities that there will be some wavelength such that all the shorter ones are absorbed. In the visible, yellow and orange and red are examples of this. There are scattering phenomena that depend on microstructure that often cause this, which is why yellows and reds are so common in nature. If it weren't for chlorophyl and the sky, they'd nearly be the only colors appearing in nature at all. This generality also applies to the ultraviolet, so that many things absorb ultraviolet and not many things reflect it. It would be unusual, then, for something to reflect ultraviolet and not visible light, just as blue objects are unusual in nature. But there certainly are some such things.

The filter on the front of a light designed to emit only ultraviolet would also be an example of an object that reflects ultraviolet and absorbs visible wavelengths.
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  #21  
Old 06-07-2008, 08:11 PM
John DiFool John DiFool is offline
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A black light (staple of Spencer's Gifts) is mostly UV, right? Looks deep purple to me.
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