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Clear Fluorescent?

It is because of how they work. The actual radiation is initially UV (IIRC), and the coated tube converts that to visible light. The coating is why they aren't clear.
 
The light you see in a fluorescent bulb is due to the coating on the inside of the glass tube. The light generated in the bulb itself excites the coating, causing it to fluores in the visible spectrum.

R
 
Belldo,

Flourescent lights and neon lights work very similarly.

Like the two other people mentioned above, the UV light produced by ionized argon and mercury inside a flourescent lamp, excites the white phosphorescent coating covering the tube. This coating then gives off a white light, which you see as the light produced by a flourescent lamp. In effect, no white coating....no useable white light.

A neon light works by having the ionized gases themselves give off the light, no phosphorescent coating invloved. I am sure that you have seen a neon sign that uses clear glass tubing. The gases inside the tube(s) glow red in the case of Neon gas. Blue in the case of Mercury. Green in the case of mercury vapor. Gold in the case of Helium (in an amber colored tube). Yellow in the case of Sodium. As you can see, none gives off a nice white light......hence the need for the flourescent lamp with the phosphor coating.
 
The reason none of these methods produce white light has to do with the nature of white light, and the physics of light production from ionized gases. White light is a mixture of different colors. There is no such thing as monochromatic (one color) white light. A neon tube, or fluorescent, works by exciting the electrons in a gas. When the electrons drop back down, they emit a photon. The wavelength of the photon (color) is precisiely determined by the energy difference between he excited and resting electron energy levels. Since all of the photons produced by a particular gas have the same wavelength, you get monochromatic light: one color. There's no way to get the mixture that produces white light. Using the phosphor coating on the tube lets monochromatic light produce white light.

Note: LEDs have the same problem, you can't produce a white LED because they are inherently monochromatic. White light from LEDs requires either three LEDS (red blue and green), or an LED with a phosphor coating.
 
Originally posted by: sgtroyer
The reason none of these methods produce white light has to do with the nature of white light, and the physics of light production from ionized gases. White light is a mixture of different colors. There is no such thing as monochromatic (one color) white light. A neon tube, or fluorescent, works by exciting the electrons in a gas. When the electrons drop back down, they emit a photon. The wavelength of the photon (color) is precisiely determined by the energy difference between he excited and resting electron energy levels. Since all of the photons produced by a particular gas have the same wavelength, you get monochromatic light: one color. There's no way to get the mixture that produces white light. Using the phosphor coating on the tube lets monochromatic light produce white light.

Note: LEDs have the same problem, you can't produce a white LED because they are inherently monochromatic. White light from LEDs requires either three LEDS (red blue and green), or an LED with a phosphor coating.
Click to expand...

Same reason you'll probably never see (at least not soon) a white laser pointer. Lasers also emit very specific wavelengths. There's even trouble producing certain colors of laser light - I don't remember if it's either blue, green, or maybe it's both, that start as a red laser, but it's passed through something that shifts the wavelength. I think I read that somewhere, and didn't imagine it.😱
 
There are blue and green lasers. I've used an argon ion laser that's in the blue-green range. Don't remember the exact wavelength. The only ones I specifically know about are gas tube lasers, though. I don't know if a solid-state (really small, like in a laser pointer or CD-ROM drive) blue laser exists yet. It's a pretty hot topic of research, because a blue laser in a CD or DVD drive would allow higher capacity. Smaller wavelength allows smaller pits=more data packed onto a disk. I think DVD's still use red lasers. Am I correct?
 
A couple of years ago, high powered, cheap blue/green lasers were the holy grail of solid state physics. Nowadays, they are still a lot more expensive and underpowered than red ones but they exist. And why can't you get a white laser pointer? Just stick 3 Lasers in a case and have them focus on a point. I imagine that they would be sufficiently close together than they wouldnt seperate over usable distances.
 
couldn't you mix neon, sodium, and mercury in the tube and get a white light as a result?
(or do the three require different physical conditions to work right?)
 
The really odd thing about laser light is that the emitted light is synchronized. When you hear about "light waves" it really applies well to lasers. It is what keeps the beam tight and focused over long distances. Actual white light, no matter how tightly focused and channeled, would not maintain a focus like laser light. An old term for lasers is "Coherent" light, meaning it stays together. All the photons are at exactly the same frequency and resonance. Therefore it is a pure color. Pure red, pure green, etc., and purchased for their specific frequency, measured in nanometers. You've certainly seen that number on the side of laser pointers.

I don't know what would happen if you focused a Red, Green and Blue laser beam together. It certainly wouldn't have a balanced spectrum like sunlight, but it might actually appear as white when it hits a surface.

 
there are a few correct posts in here and a few incorrect. in neon tubes, the exciting of the gas produces light, but in fluorescent, the exciting of the gas causes produces free electrons in all directions, which excites the phosphor coating on the inside of the tube, which produces light
 
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