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From: morrison@cs.uiuc.edu (Vance Morrison)
Newsgroups: sci.electronics
Subject: Re: incandescent light bulb life extender
Message-ID: <1990Dec4.042524.14018@ux1.cso.uiuc.edu>
Date: 4 Dec 90 04:25:24 GMT
References: <58335@brunix.UUCP> <1990Dec4.113531.10096@csc.canterbury.ac.nz>
Sender: news@ux1.cso.uiuc.edu (News)
Organization: University of Illinois at Urbana
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In <1990Dec4.113531.10096@csc.canterbury.ac.nz> elec140@csc.canterbury.ac.nz writes:

>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!)
>>

>bulbs go when you turn them on?). I imagine the discs are simply resistors,

Hugh was right (the disks are rectifiers), but the reason why they make
bulbs last longer is very simple.  Since the diode effectively halves the
duty cycle, will only consume (very roughly) half the power.  The filament
does not get as hot and thus the bulb last longer.

So why don't manufactures just build the diode in?  Because the efficiency
of the bulb goes down the lower the filament temperature.  Thus you get
long life but low efficiency.  Since light bulbs are cheap ($.25 to $.50)
and energy is expensive ($5 for a 100W bulb over its lifetime), this is
definately a false economy unless changing the bulb is a major pain.

While I am at it, the new compact flourescents have both long life and
high efficiency.  They have a higher up front cost, but do pay for themselves
with energy savings.

Vance


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