I don't know about that. My wife has two of these fire hazards. One has a
continuously variable dimmer knob, but the pot seems to have died in it.
The other has a three position switch allowing for two brightness levels.
I once heard something like you describe though, but IIRC they also said
that running it at full voltage again would restore the bulb. Anyone?
There is no definitive answer to this.
I remember looking at some book in a university library over 20 years
ago, showing lots of graphs and equations expalining what supposedly
happens to the halogen cycle when a halogen lamp is dimmed.
Supposedly, dimming a halogen lamp slows down tungsten evaporation
more than it slows down the halogen's returning of tungsten to the
Now, for a couple things going wrong:
1) Dimming a halogen lamp is likely to not extend its life as much as
dimming a non-halogen one does. The ends of the filament are cooler, and
can be attacked by the halogen cycle, causing thin spots in the filament.
These "end notching" sites can have temperature overshoot during a cold
start. Soft starting can help here (and usually helps less with
non-halogen lamps, where most fatal filament thin spots usually have
excessive temperature in steady operation, and worsen at a rate
accelerating worse than exponentially).
Such filament end notches will worsen until failure occurs there one way
The bottom line is not dimming shortening life, but dimming extending
halogen lamp life less than it does with non-halogen lamps.
2) Halogen lamps could contain contaminants that do the halogen cycle in
reverse - transporting tungsten from the filament to the inner surface of
the bulb. Such bad stuff may slow down less from dimming than the proper
halogen cycle does. In such a case, dimming to the extent where a
contaminant's "reverse halogen cycle" outruns the normal one will cause
I suspect such problems are less with halogen lamps made by major brands
such as GE, Osram/Sylvania, Philips, Thorn and Ushio. I suspect that such
lamps will take mild to moderate dimming well and *usually* (maybe or
maybe not reliably) not blacken with severe dimming. No guarantee from me!
Now, for fixing blackened halogen lamps:
I hear that this works. I suspect it works only if the blackening is
simply tungsten, as opposed to an oxide (dusty grayish or colored). I
would also be a bit leery of doing this, since with full power operation
before the blackening is fixed the bulb can overheat. Every blue moon or
something like that, a halogen lamp somewhere explodes even if nothing
wrong is done, so I am leery of doing anything that increases stress on
- Don Klipstein ([email protected]