On 12/14/2012 5:56 PM, Phil Allison wrote:

"William Sommerwerck"
"Phil Allison"

** What "issue" is that ??

There are actually two issues.

One... A halogen lamp has to run at or above the temperature at which the
tungsten is redeposited on the filament more rapidly than it evaporates.


** Irrelevant.

The TRUTH is that the re-deposited metal does NOT repair the damage done to
the filament - there are many pics that show this.

The halogen cycle merely keeps the quartz glass clean !!


This temperature is presumably well-above the temperature of a
conventional incandescent lamp. It's reasonable to assume that reducing
the filament voltage some unstated amount will lower the temperature below
the critical recycling temperature, but still high enough to cause the
filament to rapidly burn out. No one here seems to have any information
about this.


** The simple fact is that halogen lamps do NOT have especially long lives -
any more than non halogen lamps with the same filaments.

You're right about the halogen being there to keep the glass clean, but
not about the longer life. A 3400K mogul-base photoflood, like the ones
I used to use in the 1970s, has a lifetime of about 25 hours.

The high gas pressure inside quartz-halogen bulbs is what requires the
very thick quartz envelopes. High pressure slows down the diffusion of
tungsten vapour away from the hot spots, so that metal is selectively
redeposited near where it evaporated. That improves the lifetime by a
pretty useful factor like 20, and that's apples-to-apples, both 120V 500W.

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 USA
+1 845 480 2058

hobbs at electrooptical dot net
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