At 02:53 PM 8/7/02 -0700, you wrote:

Raise the voltage, and the efficiency goes up, but the life goes down.

Run a 120V bulb from half-wave rectified 240VAC (RMS voltage is
around 170V) and you get a much brighter and more efficient light bulb
that lasts maybe 10 hours rather than 1500 hours. Ten hours is a
reasonable life for a flashlight bulb, but would be unacceptably
low for many other applications.

Obviously, it takes more power to maintain the filament at a higher
temperature (see Stephan-Boltzmann, it's the fourth power of
temperature considering radiation cooling).

Moving the temperature up increases the amount of energy coming
from the filament that falls into the *visible* range of wavelengths
(see Planck's Law, Wein's Law), which is why we can say that the light
is more efficient. If you count the total energy, including IR and
UV, all incandescent lamps are 100% efficient, of course.

Life decreases exponentially with applied RMS voltage. A trade-off.
By jacking the voltage up on a regular lamp you can make it act
like a short-lived photo-flood lamp with a higher color temperature,
higher efficiency and drastically shorter life, just as you can
reduce it and get long life at much poorer efficiency.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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