TKM ) said...

For heat to affect bulb life, you have to
either have enough heat to melt the glass, crack the internal glass seal or
destroy the lamp basing cement. Think about incandescent bulbs in ovens and
other high-temperature applications.

Then why are special bulbs manufactured for those applications?

Yes, bulb filaments operate at very high temperatures, but the overall
heat buildup for the bulb as a whole has a design limit. Exceed that limit,
whithout exceeding limits that would cause a fire or do other damage, and
you will see a decrease in bulb life.

On/off operation might affect bulb life a bit when the bulb is old; but not
when the bulb is new.

It is stress, but generally has little effect on a newer bulb.

If on/off made a difference, we wouldn't see flashing
sign lamps on theater marquees.

True, but what is the total hours of operation of these lamps and how
does this compare to that of a bulb that is just left on?


All that said, a main point in my original post was that with the exception
of vibrations, it is not likely that any one factor could reduce the life
of a bulb nearly as much as the original poster was experiencing.

--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
- Napoleon
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