Interesting halogen bulb observation

evan9162

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Apr 18, 2002
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Boise, ID
I noticed something very interesting after shining my Arc-AAA UV at an MR-16 halogen lamp...the quartz bulb (specifically, the quartz its self) began to flouresce a blue-green color...observe:

hal-fl.jpg


Is this part of how halogen bulbs produce whiter light? Are they increasing the output color temperature by mixing in some blue-green light from the quartz housing flourescing under the extra UV? It would be a neat effect, not unlike how white LEDs work.
 

Chris M.

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Jan 17, 2001
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I believe it`s down to the type of quartz glass used. That one would be a "UV-Stop" type - halogen lamps put out small but significant amounts of UV light which is desirable to filter out. Lamp manufacturers mix in some stuff to the glass which absorbs it, stopping UV from ever leaving. What you`re seeing there is the glass absorbing the UV and since the energy has to go somewhere, it dissipates it by flourescing at a lower wavelength. Probably gets mildly warm too but at that sort of level, undetectable. The amount of flourescence due to the UV emitted by the lamp would be negligable compared to the light produced by the filament, but any emitted radiation absorbed or reflected back inside will only serve to make the filament or glass slightly hotter, and hence capable of burning whiter. I wouldn`t have thought by much though, compared to non-UV-Stop lamps. The only thing you might notice though is that more brighter, whiter lamps will tend to have the UV-Stop glass compared to smaller ones, because the hotter the filament burns at, the more UV it produces.

Interestingly, some halogen lamp capsules actually glow a cold blue/white for a short while after you turn them off - they just have more of the UV absorbing stuff in the glass. Not all of them are like this but it is kind of wierd to see a big spotlight glowing blue in the dark after it`s just been used.

/ubbthreads/images/graemlins/eek.gif /ubbthreads/images/graemlins/grin.gif
 

Zelandeth

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Nov 28, 2002
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I've observed that also, though in one case on a very cheap ($4) generic brand 6V spotlight, using a 4R25 battery and a standard PR-base krypton bulb. saw it somewhere else as well, though I can't at the present moment remember for the life of me which light it was...have to go through the whole collection to try and find out.
 
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