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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.

Finger oils can burn and darken, creating a hot spot on the quartz.

Yes cleaning them would be a good idea.

How prematurely? Lots of things can cause early failure. Defective
manufacturing, poor handling, excessive vibration, excessive voltage, etc.