How come we can see certain UV-Lights?

Question

I'm certainly no scientist but I understand wavelengths of energy. If Ultraviolet, Infrared, Gamma, etc. are all different wavelengths than Visible light, how come we can see certain ultraviolet lights? I've seen the ones at laser-tag arena and the ones at museums and they all look purple-ish. Is this because they are not truly ultraviolet but are a very high frequency visible light?

Answer 1

UV lamps/lights typically use a very dense filter to block off any visible light the source produces although you can buy less expensive UV fluorescent tubes that look gray when off and let the "natural" UV of fluorescent core gases come out. If used with posters, you can see the edges of the posters as well as the glow part.

The deep purple/black filter starts in the high purple and some people don't see anything at all when it is on, although most people see a deep purple light that is very hard to look at because the eye can't focus it properly, not being evolved to do that

Answer 2

Guest

Reply #2 on: 03/09/2007 13:26:30



It is no accident that the range of sensitivity to electromagnetic radiation for most animals fits the range of wavelengths that filtered / absorbed least by the atmosphere - we make use of what is most available. The amounts of IR and UV, available at the Earth's surface, vary a lot, so they are probably not worth using except in certain circumstances.

Some specialist animals - pit vipers etc, adapted to be more sensitive to infra red - to detect the warm bodies of prey.

Some insects 'came to an arrangement' with some plants and the two species use UV to signal the 'flight path' onto flowers for pollination (in Summer, when there is more than average UV around). This is a sort of niche relationship and must have advantages for both organisms.

But the majority use more or less, our visible spectrum.

Distinguishing 'colour' is useful for some animals - so they do it. For others it's not - so they don't. Three - colour analysis seems to be the best value for money - so that's what we use.

Answer 3

They emit a range of wavelengths, not just one, so even though most of the light they produce is ultraviolet some is in the visible spectrum so you can see it.



This may be deliberate, so you can see when the UV light is on. Staring at a bright UV light could damage your eyes; if it emitted NO visible light you wouldn't even know you were doing it until it was too late! The ones at laser tag should be dim enough to pose no danger anyway though.

Answer 4

I've always thought of them as bluish, and the infrared as reddish...



That said, you can't see UV or IR light directly. What does happen, though, is that they get reflected from objects at a different frequency, closer to visible light, and hence you can "see" the object. Light colours (white, yellow) are usually the ones that kind of fluoresce under UV light. So, the light directly from the source may be UV, but you can see reflections off other objects.