On 2017/06/26 9:52 PM, Phil Allison wrote:
John Robertson wrote:

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When they are RUN at the rated voltage and power. If you dim them the
tungsten is deposited on the quartz and short of heating the quarts to
white hot (above poster's remarks) the tungsten is going to STAY on the
quartz, not recoating on the filament.

http://www.topbulb.com/blog/dimming-...halogen-cycle/


** That is merely one person's opinion, not backed up with evidence.

Wiki says differently :

https://en.wikipedia.org/wiki/Haloge...on_performance

Stage lighting uses dimming all the time with halogen lamps and there is no blackening or short life experienced - the lamps run much longer as expected.

The claim that the "halogen cycle" puts metal back on the filament is true but it does not deposit it back where it came from so has little effect on lamp life.

Most halogen lamps are low voltage or high powered - so in both cases the filaments are thicker than typical non halogen examples.

Having a thick filament makes a halogen lamp last longer.



..... Phil


Well, I must confess I've never studied halogen bulbs on dimmers but
reading Lutron's site does not give any concerns from them about
halogens on dimmers in household use:

http://www.lutron.com/en-US/Educatio...ingBasics.aspx

I would like to assume that you are correct, Phil. One problem though -
your reference source says:

"With a reduced voltage the evaporation is lower and there may be too
much halogen, which can lead to abnormal failure."

and also:

"There are many situations where halogen lamps are dimmed successfully.
However, lamp life may not be extended as much as predicted. The life
span on dimming depends on lamp construction, the halogen additive used
and whether dimming is normally expected for this type."

So, perhaps theatre halogen bulbs are designed to be dimmed?

http://stagelightingprimer.com/slfs-light_sources.html

Perhaps not, they don't mind of the bulb lasts a shorter time, but want
the brightness in a compact source.

Also, are house halogen bulbs designed to be dimmed?

Philips bulbs seem to be (perhaps...):

http://www.philips.ca/c-m-li/halogen-light-bulbs

"Halogen lamps are designed to operate at very high temperatures to
ensure optimal performance. Dimming at above 60% of the rated volts can
be done. It is recommended to revert to full brightness for one minute
prior to switching the lamps off."

In other words do not run them above 60% of rated line voltage for
extended times without heating/running them at 100% for one minute prior
to turning off. I am SURE everyone will do that!

A double blind test would be nice to put this to bed.

John :-#)#