Under-driven Incan (Xenon, Krypton, Halogen) lamps : Bad or no problem?

LEDcandle

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I've read several posts here and there about underdriven incan lamps being bad for it as there is not enough heat for it to operate within spec and shortens its life etc...

Is this confirmed?

Because I am wondering if that is the case, how about the spotlights we use in our house (typical MR16 halogens from 25-100w). They usually come with dimmers which give you a full range of brightness.

Does it mean if we always turn the spotlight on low, the bulb life will shorten?

Thanks!!
 

mdocod

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generally speaking, slightly underdriving a bulb will increase it's life, where overdriving it will decrease it... however, this varies by lamp.. and severely underdriving some lamps will lead to an early demise as they need to operate within a tempurature range for the cycle of something to do with tungston evaporating and redepositing to occur... i may be way off here, lol...
 

LEDcandle

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Yeah, I heard about the tungsten thingie and stuff, that's why I'm wondering if a spotlight is constantly on dim-mode, won't that kill the lamp noticeably early... :D
 

legtu

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AFAIK, dimming is not recommended with halogen bulbs and some xenons. Dimming is fine and will generally increase lamp life with the other type of bulbs.
 

the_beast

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No idea about the xenon bulbs, but the halogen bulbs need to run at high temperatures for the halogen cycle to work (as mentioned above). As the bulb burns bits of the tungsten filament fly off and hit the glass. The halogen gas reacts with this & picks up the tungsten. When that molecule then gets near the filament again the high temperature reverses the reaction and the tungsten is deposited back on the filament.

At lower drives (and hence lower temperatures) this won't happen, and so the glass will darken. A bigger problem starts to appear though - as the filament temperature is lower, the ends of the filament (which as thicker and close to the supports and therefore cooler) is at a temperature low enough to react with the halogen. So the filament in an under-driven halogen bulb is erroded away by the gas that is put in there to prolong the life of the bulb...
 
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