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From: skwu@boulder.Colorado.EDU (WU SHI-KUEI)
Newsgroups: sci.electronics
Subject: Re: incandescent light bulb life extender
Message-ID: <30670@boulder.Colorado.EDU>
Date: 5 Dec 90 17:37:48 GMT
References: <58335@brunix.UUCP> <1990Dec4.113531.10096@csc.canterbury.ac.nz> <1990Dec4.042524.14018@ux1.cso.uiuc.edu>
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In article <1990Dec4.042524.14018@ux1.cso.uiuc.edu> morrison@cs.uiuc.edu (Vance Morrison) writes:
.... much omitted ....
>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.

Spoken like a true representative of a light bulb maker!  Since the life of
a bulb approximates:

	Life = 1 / V ** 11  (the exponent varies between 10 and 12)

while the efficiency (light output) drops almost linearly with reduced voltage,
building the diode in would only reduce the sale of bulbs.

Incidentally, a good source of long life bulbs is any electrical supply
house that sell 125volt bulbs at reasonable price.


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