[Phys-L] Re: light bulb transient

[Bernard Cleyet <anngeorg@PACBELL.NET>]

consider the claim that inserting a thermister causes lamps to survive
much longer.  I haven't seen them sold for some time.  They "were" a
disk placed in the socket, so they were in series w/ the center contact.

I've assumed the burn out on turn on was because the switch closure was
rapid and at a V peak of the supply i.e. ` 165 V.  However, the supply
is above 117 V only for about five mS. and the heating time is closer to
100 mS., therefore, this is another failed cleyet hypothesis.

Do lamps operated on 25 Hz supply have a high mortality?

bc

John Clement wrote:

> This still does not resolve the possibility that there is a flash when a
> bulb burns out.  It is quite possible that there is local reduction in
> resistance at the time the bulb is ready to burn out, and an increase in
> temperature.  One can simulate this effect by carefully tapping a bulb to
> short out some of the coils.  It will burn very brightly for a limited
> period of time.  Guys used to do this with hall lights in the dorms.  Also
> there is seems to be a definite tendency for bulbs to burn out when first
> turned on, so there is likely some transient effect.  It may actually be the
> rapid heating and consequent fast thermal expansion that causes bulbs to
> burn out.  Once a bulb is "lit" the thermal changes are not as severe.  A
> possible scenario is that the rapid thermal expansion may cause some coils
> to shift and short which produces lowered resistance, a flash, and burn out.
> Presumably ramping up the power via a dimmer might make bulbs last longer.
>
> Simulating this type of effect is fairly difficult.  One might be able to
> observe shifting of the filament when the light is turned on quickly.  OTOH
> maybe the manufacturers have written some papers on these effects and their
> solutions.
>
> John M. Clement
> Houston, TX
>
>
> > I salute the experimental data adduced by John and Mike.
> > I question the use of AC if the impetus is to investigate localized
> > overheating in bright spots at the turn on transient though.
> >  DC would show variations a little better?  In the experimental
> >  subjects,  it is clear that turn on flash is not seen.
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