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Re: Cooling down light fixture? or Some cats are just too cool

A couple of points I meant to put in my last post but

I assume your T12 and PC fixtures are in separate
enclosures.  The AllGlass fixtures are generally
extensively tested and I wouldn't expect their T12 fixtures
to produce a lot of heat in the small space of the hood,
even though it relies on convection cooling.  Measuring the
temp wouldn't be a bad idea, so long as you had a
thermometer that reads well past a couple hundred or so
degrees F.  You'll probably find that the T12 fixture is
not very hot -- between 80 and 100 or so degrees at most. 
Cooling that fixture would probably reduce the the light
output without having a significant impact on bulb life. 
the variability in bulb life span is affected by a number
of things, and a few degrees within the normal dsign
temperature range isn't going to change your life or the
length  of that of your bulbs'.  But lowering the temp
below the design temp for full vaporization of the mercury
is going to reduce the light output, even though your tank
won't be apreciably cooler.

PCs pack more watts into less space than T12s (at least the
way that AllGlass drives T12s ;-)  ) and can present more
of a heat concern, depending on the number of lamps you
squeeze over a tank.  AllGlass PV fixtures don't squeeze a
lot of lamps over a tank.  AllGlass won't put two PCs side
by side in a hood and I suspect that heat is one of the
reasons -- they want to avoid any potential heat issues for
their customers (their market includes a lot of folks that
don't want to fiddle with their equipment or have new
equipment present new issues.)  Anyway, compared to the T12
fixture, the PC fixture is more likely to be adding more
heat, faster, than your tank can get shed it.  But if it's
a single PC in a hood, like an AllGlass PC, then you might
consider a simpler solution to reduce tank heating -- put a
moderately sized room or desk fan in the room blowing on
the tank.  Some folks find that gives them enough cooling
in those hottest months of the year when heat is an issue. 
It avoids all of the modifications to the hoods.

Good luck,
Scott H.

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