Quote:
Originally Posted by infernalis
You have that backward, mercury vapour lamps were invented 30 years prior to metal halide lamps.
A mercury vapour lamp has no halides (metal salts) in the plasma arc tube, Metal halide lamps are mercury vapour lamps with an additional metal salt compound (halides) added to the amalgam to broaden the spectral output.
One of the factors that caused experimentation with the arc tube contents was that a raw mercury vapour lamp output very high UV that would be harmful to stare into the bulb for any length of time, The first solution was to coat the glass envelope (outer bulb) with a UV reactive phosphor, that's how modern day florescent bulbs were born... the main difference between a florescent bulb and a mercury vapour bulb is the gas pressure inside the lamp. A MV lamp has very high pressure inside the arc tube, and generates such an intense heat that the amalgam must be contained in a quartz tube as the temperatures achieved in operation will melt standard silica glass, the low pressure content of a florescent lamp generates far less heat, so standard glass works fine.
However, the phosphor coatings were inefficient compared to doping the mercury itself, this is why we almost never see a frosty white coating on a metal halide lamp, but almost always see a frosty white coating on mercury vapour lamps.
From a manufacturing standpoint it's cheaper to make the metal halide lamps, a minuscule grain of halide salt is a lot cheaper than a whole coating of phosphorescent materials, and less harmful to the environment when the lamp is no longer usable.
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I see interesting - i think perhaps I have been mis-sold a halide lamp as a mercury vapour, I have one which has Xenon mentioned in the specs, and is clear glass, but I bought it as a mercury vapour, turned out to be useless in my paludarium (no growth whatsoever) and I switched it out for 6000K LED's, always wondered why!
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