Don Klipstein
Guest
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 Posted:
Tue Nov 29, 2005 12:17 am Post subject:
Re: What bulb voltage? |
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In article <43822FB1.2000007@netscape.net>, mike wrote:
| Quote: | John Popelish wrote:
Richard wrote:
(snip)
If when the overated lamp is burning I read 2.4v, 0.3A, then surely
I'd need
a lamp with those specs?
That process would specify a lamp that would run at rated filament
temperature and that would consume the same power from the battery. It
would also produce less light than the bulb that was running well above
its ratings.
Electrical power to light power conversion efficiency goes up
dramatically as filament temperature rises. But life expectancy goes
down dramatically, also.
I can't find the reference, but as I recall, there is a twelfth power
somewhere in that equation...dramatically indeed.
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Life expectancy varies inversely proportionally with voltage to the 12th
power.
Light output varies proportionately with voltage to the 3.2-3.5 power.
Current is usually close to proportional to square root of voltage.
This "rule" for tungsten incandescent lamps, however, is a
"1-size-fits-all" and is only approximate, and holds up better for
"reasonable" applied voltages.
Now for one more bit on design voltage of incandescent lamps to be used
with batteries: It is common to have the design voltage only around
1.2-1.25 volts per cell. Not only is resistance of the cells a factor,
but also the open circuit voltage of a cell that is halfway used up is
less than 1.5 volts.
Keep in mind that flashlight lamps usually have a design life expectancy
of only 15-30 hours or so at design voltage.
- Don Klipstein (don@misty.com)
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