On Fri, 09 Dec 2005 22:53:49 GMT, "TKM"
wrote:

I wonder how great the advantage is relative to 115 and 230. I
wonder if DC is better than AC. With modern semiconductors, would
it be worthwhile to build lamps to supply the ideal voltage for an
incandescent bulb of a certain wattage?

One popular type of desk lamp uses an automotive brake bulb and a
12V transformer. Is 12V better than 50 for a bulb of 20W or so?

A-line lamps are fairly well optimized given the requirements to operate on
the 120 or 240 volt supplies since designers have had about 100 years now
to work on them. After the basic material properties are known and
accounted for, then manufacturing details begin to be the important
determinants of performance. How uniform is the filament? How should the
coil be mounted to minimize shock/vibration? What sort of seal should be
used? How pure must the gas fill be? Etc.

I doubt that it would be worth developing a comprehensive "optimized lamp
design" at a non-standard voltage and then use electronics to obtain that
voltage from the line since the performance of lamps now is probably within
a few percent of optimum anyway and there are losses in transformation.

I agree with your statement in the first paragraph - if we
are constrained to operate to 120 or 240 volts. However I
disagree with your later statement that lamp performance is
within a few percent of optimum - if we are allowed to
change the operating voltage. I do, however, agree that it
would not be worth if from an economic point of view to
develop a disposable voltage converter for incandescent
lamps.

Someone did try to put a diode in the base of each lamp to
reduce the RMS voltage from 120 volts to 84.9 volts. This
does increase efficacy at low cost, and if half the diodes
are inserted one way, while the other half are inserted with
opposite polarity, there should be no net effect on the
power grid or metering. However, this option opens the door
for crafty people to select lamps with all the same polarity
and hence get part of their power for free, so this idea was
dropped, I believe under pressure from the power companies.

Traditionally, AC has been thought superior to DC operation of incandescent
lamps because so-called filament "notching" can occurr on dc plus if there
is any moisture present in the base/seal area, metal can electrolytically
move from one line to another and cause seal or line failure.

So, life with AC is better than with DC, but the switch from
one to the other does not effect efficacy. In fact, the RMS
voltage of an AC waveform is defined as the DC voltage that
gives the same heating power - and we all know that
incandescent lamps are just heaters that happen to generate
a bit of light.

--
Vic Roberts
http://www.RobertsResearchInc.com
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