Re: Does an automatic shutoff energy saver light switch exist?

[VWWall <vwall@xxxxxxxxxxxxxxxxx>]

Steve Lockridge wrote:
>
> I have a question about turning lights on and off.  I have been told
> that leaving a light on maximizes its life and turning it on and off
> frequently will shorten its life.  Is this true?  My background is in
> transformers and it is better to leave them running than to shut them
> off.  Of course, we're talking about several thousand volts versus a
> 120V light bulb.  Thanks.

A tungsten filament lamp almost always expires the last time you turn it
on. (Sort of like why you always find something in the last place you
look.)  The current surge in a cold filament and rapid expansion causes
the failure.  The total time before this last gasp is probably about the
same even if the lamp is cycled on and off.

So if it were left burning, it's total hours would be longer than if you
had not turned it off, and then on, the last time.

Fluorescent lamps rely on a starter mechanism which degrades with use.
They may benefit from fewer on-off cycles.

As an aside, in the UK and other 240V lighting countries, an expiring
lamp will often cause a large enough "plasma arc" to take out the
circuit protection.  Hence the lamps commonly include an "internal
fuse".  This not needed at 120V.

--
Virg Wall, P.E.