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Re: Cooling Lights and making light of worms or worms of light

Chuck H, the worm conquerer, said:

> I recently bumped into this article from an architectural
> publication 
> ("Progressive Architecture" Aug. 1992, p. 89-92) that has
> a nice little 
> chart showing the effect of heat on the efficiency of
> typical compact 
> fluorescent bulbs.  The chart is labeled figure 3 and is
> about a third of 
> the way down the page:
> http://www.nrc.ca/irc/practice/lig3_E.html
> The article states that 38 degrees Celcius (100 F) is
> considered optimum 
> for typical CFL's.  A temp within 15 degrees C of optimum
> (~85 - 120 F) is 
> still giving you better than 90% efficiency, though it
> appears that warmer 
> is definitely better once you pass that range.  It is
> also stated that it's 
> the coldest spot on the bulb that determines the light
> output.  This makes 
> perfect sense, but I'd never really thought about it
> before.

A fluorescent bulb is designed so that the mercury inside
it "evaporates" into a plasma.  If the bulb is too cold,
some of the mercury will remain liquid and the plasma will
not conduct as well, lessening light output.  So why not
just burn them hotter?  Once all of the mercury is turned
to gas, more heat won't increase the mercury content of the
plasma, so there is a diminishing return.  Also, more heat
will cause the electrodes (the filaments) to evaporate
faster, giving faster blackening of the ends as the
filaments hurry towards their final reckoning.  More heat
also increases the pressure inside the bulb, which drives
more of the mercury right into the glass where it can never
again do any good at all -- and you thought glass was
impervious ;-)  

Flo bulbs are made to operate within a range, the engineer
choosing a mix of compromises in performance
characteristics and durability.  You can play with these to
advantage (and disadvantage) by overcooling, undercooling,
overdriving, etc.

On icy cold mornings, if you turn on the fluorescent lights
in the garage, they might seem dim to you even if you don't
have electronic ballasts (which usually aren't designed to
operate at very cold temps) -- those chilly bulbs are dim,
but the will brighten if they can warm up enough.  If they
are way too cold, they won't have a properly charged plasma
and will show dark "waves" sliding across the bulb as the
plasma cannot maintain a full charge.  Some folks call
these "waves" fluorescent wiggly worms -- which makes it
fitting that Chuck H commented on cold flos, what with his
withstanding so much Klez and all.  :-)

Scott H.

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