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Why name them "black cathodes"?

T

TownRanger

n00b
Joined
Jul 9, 2006
Messages
26
So this evening I was taking a look in an automobile assessory shop. They mainly sell lightings and spray cans. I saw two tubes labelled "Black Cathodes".

I asked the attendant. He knew nothing. "Purple light," he told me.

Is there such a thing called "black cathodes"? I guess from the picture on the package that their lighting looks exactly like UV tubes. Pity I didn't take a picture of it.
 
I have never heard of "black cathodes", but black lights are always UV lights, like mwarps said. They almost always label them UV cathodes.

The reason they are called black is because the incandescent UV lights don't even seem to emit light (it is a very low purple glow) until you see the light get reflected back...
 
synaps3 said:
I have never heard of "black cathodes", but black lights are always UV lights, like mwarps said. They almost always label them UV cathodes.

The reason they are called black is because the incandescent UV lights don't even seem to emit light (it is a very low purple glow) until you see the light get reflected back...
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Or touch the bulb itself, Those things get extremly hot!
 
FIDDYOWNZ said:
Isn't that the definition of reflection? ;)
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Nope... They're very, very different!

UV light works by exciting a phosphor atom to a higher than-normal energy level. The atom's natural affinity to remain at a constant normal level forces it to emit energy (in the form of a photon) in a wavelength we can see. Other types of phosphors can't re-emit photons as easily, so they remain "charged" for a few minutes... Randomly spewing out photons whenever they can. This is what we call a "glow in the dark" phosphorus coating.

Reflection can occur on ANY surface of sufficient uniformity. metals, plastics, anything with a flat enough coating will reflect and refract a certain proportion of incoming photons... They don't absorb them at all (or at least, they don't absorb any of the ones the reflect ;))
 
Arcygenical said:
(or at least, they don't absorb any of the ones they reflect ;))
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The difference between the ones absorbed and the ones reflected (if the source is white light) is what gives the object its colour. If it isn't white light, it results in an apparent colour. The photons absorbed add to the heat of the object.
 
Michael Daly said:
The difference between the ones absorbed and the ones reflected (if the source is white light) is what gives the object its colour. If it isn't white light, it results in an apparent colour. The photons absorbed add to the heat of the object.
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yep...
 
They are called black lights because of the black uv pass filter coating put on the tubes. They allow the uv out but not the visible light. And since black is the absence of visible light...

And they heat up more because of the visible light being stopped at the coating adds up quickly in terms of heat. Like a black shirt compared to a white one.
 
yeah but wouldn't it be easier to say that it reflects? You go around giving them that kind of definition and you'll probably get beat up :p
 
FIDDYOWNZ said:
yeah but wouldn't it be easier to say that it reflects? You go around giving them that kind of definition and you'll probably get beat up :p
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Being ignorant, uninformed and uneducated is cool! Down with knowledge!
 
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