In article , Phil Munro wrote:
Don Klipstein wrote:
In art. , CL (dnoyeB) Gilbert wrote
in part:

you can try installing a dialed dimmer switch. or see if you can find
any of those devices that go in the socket that are supposed to extend
the life of the bulb, not sure what they do.

could it be the room temperature is too low? Soft starting of lights
definitely extends the life.

Usually not much (there are some exceptions), despite lightbulbs
typically blowing during a cold start.

What usually happens is that cold starts do surprisingly little damage
to the filament, while a filament that is approaching end-of-life (due
mainly to operating hours and filament temperature during steady
operation) becomes unable to survive a cold start a little before becoming
unable to survive steady operation.

A filament that has suffered uneven evaporation to the extent to become
unable to survive a cold start is already in bad shape, and this condition
is accelerating at a rate that increases worse than exponentially while
the filament is running.

Now a bit of specific data: I actually got one of those soft-starting
"buttons" to attach to the bottom of a lightbulb to supposedly double its
life. I managed to get an indirect reading of voltage drop across the
"button" and the lightbulb while the "button" was in place and fully
warmed up, and it turns out the "button" dropped enough voltage to dim the
lightbulb enough to extend its life 50%. Also: Using the usual rules of
lightbulb performance as a function of voltage, light output went down 11%
while current consumption (and power consumption, counting watts
dissipated in lightbulb and button combined) went down 1.7%.

- Don Klipstein )

Lots of nice info there. Thanks. I am wondering what the effective
voltage drop would be for a dimmer that is full on.

It has been my experience from work with tungsten heating coils in a
vacuum system that unused tungsten can be bent into small radius turns,
BUT, after it has been used into the dull red heat range the same wire
will break if that same bending is attempted. I guess it has to do
with annealed or not annealed and work hardening, but I can never
remember how that goes!

My point is that a USED bulb filament is mechanically fragile, AND
when standard service bulbs are turned on with a switch, there are
MECHANICAL forces due to the start up of magnetic/electric fields.
These mechanical forces on the filament may be demonstrated by the
ringing sound some filaments will make when a dimmer is set low. Sound
is due to a mechanical phenomenon, so that would mean the filament is
vibrating!

Outright true, but for most lightbulbs this stress is within the
"endurance limit" (threshold of causing metal fatigue), and less than the
stress of having people dance or dribble basketballs on the floor above or
slamming nearby doors. And yes I do know that a lightbulb experiencing a
cold start can have its filament mechanically jolt enough to produce a
"ping" sound that is often audible within a foot or two away.
NOTE - the filament is much weaker when hot, and the main mechanical
stress of a cold start occurs when the filament is not so hot, and much
stronger than a hot filament whether it is ductile or brittle.

I continue to be convinced that using an up/down dimmer (one with no
abrupt on/off) slows down bulb burn out, and that mechanical actions
will also do it for bulbs. For example, rough service bulbs last longer
in mechanically rough service, and if we look at the guts of such bulbs,
we see extra filament supports which minimize vibration. --Phil

Most dimmers when turned all the way up will reduce RMS voltage to a
lightbulb roughly 2-3 percent, and that reduces light output about 3 times
that and can account for a life extension of 20-40%.

In general, "rough service" bulbs have much longer life expectancy than
"standard" bulbs even where there is no damaging vibration present due to
the filament being designed to run cooler, since most such bulbs are used
where labor has to be paid to replace them. Also, they are less efficient
to such an extent that a 60 watt "standard" bulb usually outshines a 75
watt "vibration resistant" or "rough duty" one.
Over 1,000 operating hours, 15 watts of electricity usually costs more
than a lightbulb does.

--
Phil Munro

- Don Klipstein )