"Jim Yanik" wrote in message
.. .
"TKM" wrote in
:




It's an urban legend that bulb life of halogen lamps is shortened by
finger oil. The surface of the bulb may degrade somewhat where dirt
and oil react with the quartz; but that doesn't affect bulb life only
the appearance of the bulb.

TKM


I do not believe this "urban legend" claim;can you provide any proof?

It's not that dirt or oil react with the quartz,it's that they carbonize
and create hot spots,and then absorb more heat.

--
Jim Yanik
jyanik
at
kua.net

Hmmm. Never heard that one. There are already hot spots along the surface
of a halogen lamp due to filament supports and circulating gas currents.
They don't affect lamp life. What does is the temperature of the lamp seals
(where the filament wire comes through the quartz). Overheat those and the
seal cracks letting in air and the lamp fails.

But, the concern about finger prints is confusing. Strangely, Philips says
that lamp life will be shortened; but GE and Osram-Sylvania don't. Take a
look at the respective caution notices packed with halogen lamps or printed
in lamp catalogs.

I was part of the product service group for a large US lamp manufacturer for
a number of years shortly after the tungsten halogen lamp was introduced in
1958. We tested halogen lamps of 50-500 watts for general lighting service.
Dirt, fingerprints, etc. never did anything more than make a slight haze on
the surface. In a highly-tuned optical system that might cause light
distribution problems, but it doesn't affect lamp life.

TKM