Our track lighting uses a special dimmer designed for this purpose.
Additionally it uses a high tech transformer (essentially converts line
input to high frequency so it can use a smaller transformer). I just went
to a lighting store and they sold me the appropriate stuff. NOT CHEAP but
lights etc were what the wife wanted.


"TKM" wrote in message
...

"David Nebenzahl" wrote in message
.com...
Client wants to install some low-voltage halogens with a dimmer. Is this
OK? I know the dimmer will work, since the lamps are a resistive load,
but I'm not sure the halogens want to work on reduced voltage. Anyone
know for sure?


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Not a problem. There are a couple of things to know, however:

- Use the proper dimmer. Low voltage halogens require either a
transformer or electronic voltage reducer. Use a dimmer that's compatible
with what you're using.

- Halogens don't care if they are dimmed. At full power halogen lamps are
designed to utilize a tungsten recycling process which keeps the inside of
the bulb clean. The gas chemistry inside the bulb recycles the tungsten
that would ordinarily deposit on the bulb surface back onto the filament.
If you dim the lamp, the halogen cycle stops; but that's O.K. The
filament is operating at a lower temperature and not throwing off much
tungsten anyway. Some wonder if there is some kind of "forbidden zone" of
operation -- a dimmer setting where there is still filament evaporation,
but where the halogen cycle is not operating so the bulb darkens and
perhaps fails. According to the lamp engineers that I've talked to,
that's possible, but not likely in general lighting lamps. But if it
should happen, (you will be able to see the filament tube with a black
deposit on the inside surface) simply operate the lamp at full power for a
few minutes to restart the halogen cycle.

I have a house with several dimmer-controlled track lighting systems which
use numerous 120 volt PAR20 and 12 volt MR16 halogen lamps for
downlighting, accent lighting, etc. These systems are operated 6-10
hours/day at various dimmer settings. I used transformer-powered fixtures
for the MR16 lamps. There is no noticeable noise, even when the dimmers
are at the lowest setting, unless the house is absolutely quiet (not a
normal situation). I've not had any 12 volt MR16 lamps fail during the 3+
years that the system has been installed. The lamps have a life rating of
5000 or 6000 hours, so I'm starting to expect a few failures.

The 120 volt PAR20 halogen lamps are very sensitive to physical shock.
I've had those fail when I simply adjust the fixture and happen to shake
the fixture. What happens is that some filament coils short together and
put too much voltage on the rest of the filament. (you can see the
filament move when you look at the light beam). Now, I dim the lamp and
move the fixture very carefully and replace lamps with the power off.

TKM