"Calvin Henry-Cotnam" wrote in message
...
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?

The only thing different about oven bulbs is that they have high-temperature
basing cement so the base won't come apart and stick in the socket when the
bulb is replaced. They may also have a a smaller glass envelope than
similar wattage lamps made for general lighting service.

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.

As I said, that's a widely-held opinion, but the tests reported in lighting
journals, papers, etc. don't confirm that bulb life is reduced until the
glass softens or a seal cracks and lets in air. That's not likely to happen
in a situation where the fixture just seems to be hot to the touch even if
there's some smoking or deterioration of the fixture finishes.

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?

That's with the total "on" time taken into account.

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.

Agree. There's something else going on here. It sure sounds like poor lamp
quality and I'd like to see what happens when the OP tries another brand or
type of bulb.

TKM