On 12/12/2012 12:55 AM, John Larkin wrote:
On Tue, 11 Dec 2012 09:18:37 -0800, "William Sommerwerck"
wrote:

We run a halogen (over our dinner table) from a dimmer.
We seldom use it at full brightness. It's about 10 years old
and still on the original bulb.

The envelope is probably black by now. Incandescent life goes with
something like the 12th power of, er, power, so it's not surprising.
You'll probably find that it won't last all that long, now, at full
power. Its filament is now on the inside of the envelope.

Actually, it's the 12th power of voltage.

Even a slight drop in voltage causes a big increase in life. For example, a
5% reduction almost doubles the lamp's life (1.85 times). At a 10%
reduction, the lamp lasts 3.5 times as long.

I guess the question becomes: is there some voltage a bit below normal, where
the halogen cycle doesn't work and lamp life actually degrades? I'm guessing no.



The bulb envelope cleans up if you run it at full power for awhile anyway.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net