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From: elec140@csc.canterbury.ac.nz
Newsgroups: sci.electronics
Subject: Re: incandescent light bulb life extender
Message-ID: <1990Dec4.113531.10096@csc.canterbury.ac.nz>
Date: 3 Dec 90 22:45:31 GMT
References: <58335@brunix.UUCP>
Organization: University of Canterbury, Christchurch, New Zealand
Lines: 31

In article <58335@brunix.UUCP>, hleaves@ruby.vcu.edu (EAVES,HUGH) writes:
> Radio shack sells small conductive discs that attach to the bottom of 120v
> incandescent light bulbs. They claim that these discs will extend the life of
> your light bulbs up to 100 times. Does anybody know how these work? My theory
> was that a rectifier in the base would prevent the reversal of the magnetic
> field in the bulb due to the AC polarity change. This might reduce fatigue on
> the filament. (Just a guess, don't flame me for being stupid!)
>

I don't think it's anywhere near that complex. What destroys incandescent light
bulbs is turning them on and off. A cold bulb filament is almost a dead short,
hence the initial current thru a bulb when it's turned on is very high,
although this quickly reduces down to the design value as the filament heats
up. It is this initial high current that blows bulbs (notice that almost all
bulbs go when you turn them on?). I imagine the discs are simply resistors,
with a resistance much less than the steady state resistance of the light bulb
(hence they will have negliable effect once the bulb filament is up to
temperature), but greater than the initial resistance of a cold bulb which will
limit the startup current.

Basically they would provide a soft-start facility for light bulbs!

--
*********************************************************
Chris Kaiser
Postgrad - Elec Eng Dept
Canterbury University
Christchurch, NEW ZEALAND

E.MAIL: c.kaiser@elec.canterbury.ac.nz
*********************************************************


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