How do they work? What exactl causes them to make white objects glow such a beautiful purple?
WHo discovered them anyway?
It’s ultraviolet light. It causes fluorescent substances to glow. Since it’s easier to make things glow than to make them perfectly clean and white, most white clothes and white paper contain fluorescent dyes. Laundry detergents can add even more flurescent dyes to clothes.
Wait a minute - I thought humans couldn’t see in the Ultraviolet, yet clearly, people can see something flourescing under a blacklight. So is this reflected light really not UV, or what? If it’s not, what mechanism causes the wavelength shift?
Fluorescence is the phenomenon where a substance can absorb UV light and emit visible light. The mechanism has to do with the available energy states in the substance. You can regard the possible states as an energy “ladder”. When the substance absorbs a UV photon, a chemical bond will “jump” its energy state upwards, skipping a few rungs on the ladder. The bond will then relapse to its old energy state via the rungs it skipped, emitting lower energy (visible) photons as it does so.
For example - absorb a UV photon, energy level goes up - emit a green and an IR photon (for example), energy level goes down again. This would be a substance which fluoresces green under UV.
This is nice, but none of you are answering my question.
Fluorescence occurs with many different kinds of electromagnetic radiation, not just ultraviolet radiation and visible light.
Breifly, when one color of light hits that material, another color of light is emitted. Here’s an example: A highlighter’s ink is struck by a color of light called ultraviolet. Human eyes cannot detect ultraviolet. When the highlighter’s atoms are struck by the ultraviolet color, it causes them to emit another, different color of light. In the case of our hypothetical highlighter, the color that is emitted is yellow. I am not sure if these are the actual colors involved in highligters, but the example should help you grasp the concept. It is important to note that if we put the highlighter in a completely dark room where no ultraviolet colred light could hit it that the hightlighter would no longer emit yellow colored light.
A black light gives off the ultraviolet light that causes certain materials to give off different colored light.
All forms of ultraviolet light cause sunburns and are linked to skin cancers.
Here is a breif explanation of fluorescence. That link will probably help you understand.
Remember: a black light’s role in all this is to provide the ultraviolet color of light that causes some materials to fluoresce, as normal indoor lighting does not emit significant amounts of ultraviolet colored light.
Not all white objects do this. It’s mainly with white clothes, and, as was mentioned, it’s due to the detergents we use. As white clothes get old, they turn yellow. To make them white and bright again, detergents include molecules that absorb UV and emit blue light. The blue cancels the yellow, thus white. There’s enough UV around normally to make enough blue to cancel the yellow. Blacklights are just stronger UV emitters, so you see the blue.
So I’d say we’ve covered the first two questions well. As for the third, I have no idea. I doubt it’s been recorded anywhere, frankly. I guess you could credit scorpions, since most of the flouresce in UV.
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*Originally posted by Smeghead *
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Hey there Smeg. Out of curiosity, are there some similar molecules in toothpaste? I’ve noticed some people’s teeth are affected by black light as well. Later all.
I’ve heard that, rob, but I’d hesitate to say for sure one way or the other. IIRC, it may have been tried and abandoned at one point. I don’t have any hard data, though.
Oh, come now, fluoresence was a hot research topic in late 19th century physics, and there’s lots of material on Becquerel, Roentgen, Crookes, etc. having fun in the laboratory with it. They built apparatus of various sorts.
Look up “phosphoroscope” or “crooke’s tube”.
Turned up this: http://wings.buffalo.edu/academic/department/anthropology/Lithics/uvfa-ms.html. Good historical background.
Dagnab it. This board’s automatic URL parsing is biting again. Don’t include the period at the end of the sentence.
vBulletin really needs to do a better job of this. There are pathological cases which make it impossible to do perfectly, but it should not have done that. The mailer I use parses URL syntax and doesn’t get tripped up by things like this, for instance. In this case, once you’ve parsed off the extension part of a path component, another period should not belong to the URL, and should be seen as a terminator.
According to Cecil, teeth fluoresce naturally.