Bulbs & Lamps?
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Monsters_Inc
Banned
Gases such as Xenon (as opposed to say, the halogens) are fairly unreactive. That means a higher temperature is needed to boost its energy sufficient for the reaction to take place - in this case reacting with the tungsten filament.
Consider dissolving a teaspoon of sugar in cup of water, without stirring. When water is cold, sugar dissolves slowly. When water is hot, it dissolves much quicker.
Consider dissolving a teaspoon of sugar in cup of water, without stirring. When water is cold, sugar dissolves slowly. When water is hot, it dissolves much quicker.
Jonathan
Enlightened
'Xenon' fill tungsten lamps are actually _halogen_ lamps.
The fill gas in a halogen lamp is a mixture of a halogen (Fluorine, Chlorine, Bromine, etc.) and an inert gas (Argon, Neon, Krypton, Xenon).
The Halogen is there to react with the Tungsten, specifically any Tungsten that deposits on the envelope. This Tungsten-Halogen compound is a gas, and it gets dissociated by the heat from the filament, releasing the halogen and re-depositing the Tungsten on the filament.
The inert gas is there because at higher _total_ pressure, the rate of Tungsten evaporation is reduced. The combination of the Tungsten-Halogen cycle re-depositing Tungsten on the filament, and the inert gas preventing evaporation in the first place, means that you can operate the filament at higher temperatures for higher efficiency.
Why Xenon rather than a cheaper inert gas? Because the higher the gas pressure, the greater the thermal conductivity of the gas, and the more heat that is carried away from the filament by conduction. The _heavier_ the gas, the lower its thermal conductivity. Xenon is the heaviest of the inert gasses used in halogen lamps. (Radon would be heavier, and thus at the same pressure there would be even less in the way of conduction loss, but it has other issues.)
-Jon
The fill gas in a halogen lamp is a mixture of a halogen (Fluorine, Chlorine, Bromine, etc.) and an inert gas (Argon, Neon, Krypton, Xenon).
The Halogen is there to react with the Tungsten, specifically any Tungsten that deposits on the envelope. This Tungsten-Halogen compound is a gas, and it gets dissociated by the heat from the filament, releasing the halogen and re-depositing the Tungsten on the filament.
The inert gas is there because at higher _total_ pressure, the rate of Tungsten evaporation is reduced. The combination of the Tungsten-Halogen cycle re-depositing Tungsten on the filament, and the inert gas preventing evaporation in the first place, means that you can operate the filament at higher temperatures for higher efficiency.
Why Xenon rather than a cheaper inert gas? Because the higher the gas pressure, the greater the thermal conductivity of the gas, and the more heat that is carried away from the filament by conduction. The _heavier_ the gas, the lower its thermal conductivity. Xenon is the heaviest of the inert gasses used in halogen lamps. (Radon would be heavier, and thus at the same pressure there would be even less in the way of conduction loss, but it has other issues.)
-Jon
Doug S
Flashlight Enthusiast
Jon, I could be mistaken, but I believe that in addition to the halogen lamps that use xenon as the inert filler, there are also some non-halogen lamps using xenon as the filler. BTW, to the best of my knowledge, of the available halogen elements, only bromine and iodine are used in halogen cycle lamps.
Doug S
Flashlight Enthusiast
<font size="2" face="Verdana, Arial">None in the chemical sense of the word reaction.
Zelandeth
Flashlight Enthusiast
If I remember correctly, there's a comprehensive explanation of the processes and principles behind this somewhere within Don Klipstein's (spelling?) website.
http://misty.com/people/don/index.html
...among a LOT of other comprehensive information.
http://misty.com/people/don/index.html
...among a LOT of other comprehensive information.
