🚀 go-pugleaf

In article <7200047@silver> commgrp@silver.bacs.indiana.edu writes:
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>
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>I am looking for references and formulae for light output and color 
>temperature vs. filament life for tungsten-halogen lamps, in terms of 
>percent of rated voltage and lifetime.
>
>I want to use (relatively inexpensive) 12-volt automotive quartz-
>halogen bulbs in portable (dc) configuration where I need maximum 
>illumination.  Automotive bulbs are designed for long life in a high-
>vibration environment, leading me to believe that I can increase the 
>voltage substantially and trade-off bulb life for extra light. (I can 
>minimize thermal shock by increasing the voltage above rated value 
>after the filaments are already hot.)  

I have a study around here somewhere published by Westinghouse about
20 years ago that developed a formula for relating operating voltage
to life.  I don't remember the exact details but I DO remember that
there was a 13th power term in the voltage equation.  In other words,
life declines FAST with increasing voltage.

Automotive bulbs acheive a good life by running at a much lower temperature
than, say, a photographic lamp.  If you goose one of these bulbs up to get
the color temperature up to photographic values, the life will become similiar
to the photographic lamps.

Which begs the question.  If you need bright, white light, why not use
12 volt nominal halogen photographic lamps instead of mucking around
trying to figure out what voltage is necessary to make an automotive 
lamp run at the proper color temperature?  These bulbs are quite similiar
to the H-x automotive bulbs and not much more expensive.  The ones with
integral reflectors are very nice in that the coating on the reflector is
IR-transparent which means the light is very cool.

>
>Is it desirable to heat-sink the bulb base or to protect the lamp from 
>wind?
>

It will depend on the bulb.  In general, you want to avoid thermal
transients and excessive heating of the glass/metal transitions of
the terminals.

BTW, I've been using souped-up halogen lamps for photographic purposes
for years.  I'm using the 500 watt tubular reflector type lamps commonly
used to illuminate buildings or yards.  You can buy them at the hardware
store for a few bucks.  I use a boosting transformer to boost the
voltage to about 160 volts.  Fine tuning is done with a variac.  This
produces GOBS of very white light with reasonable lamp life (~ 100 hours
or so).  Kinda tangent to your question but somewhat similiar.

John

-- 
John De Armond, WD4OQC                     | The Fano Factor - 
Radiation Systems, Inc.     Atlanta, GA    | Where Theory meets Reality.
emory!rsiatl!jgd          **I am the NRA** |