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jakdedert

wrote:
These are 40W Wagner 795 halogen bulbs used in an automotive light
bar. They failed prematurely. We were very careful installing them
that they were never touched by hand. So I have some questions:
1. Why is it that touching halogen bulbs can decrease their life? This
is a sealed bulb.
2. Should we clean them with 99% isopropyl before installing them?
3. Does anyone have any ideas as to why these failed prematurely?
Thanks, Lenny.

The failure of a halogen bulb from finger oil is only from touching the
actual quartz is pretty immediate. The envelope either cracks...or
better yet, begins to soften at the point of finger contact and swells
like a balloon until it fails.

If you are merely experiencing shorter life than you expected, there
could be any number of reasons. One reference specifies that this lamp
should only be used in horizontal applications and that expected life is
only 200 hours.
http://www.donsbulbs.com/cgi-bin/r/b.pl/795%7C12.8v%7C3.9a~usa.html
That's not much, compared to most automotive applications. By 'light
bar', I assume you mean some kind of off-road aftermarket auxiliary
lighting installation. That would imply a more rigorous than normal
application, subject to a lot of vibration and shock.

Given a 200 hour rating under 'normal' conditions, I believe this might
be your answer. In any case, it's never a bad idea to clean the
envelope when installing. Many manufacturers supply an alcohol 'wipe'
for the purpose.

jak