Re: Cooling down light fixture?

["S. Hieber" <shieber at yahoo_com>]

Giancarlo asked:

> A little while ago there was an interesting thread about
> which direction a
> cooling fan should be blowing air into a light fixture. I
> have a mixture of
> T-12 and CF lighting on my tank and this thread made me
> think about the heat
> generated in the light fixture which originally came with
> the tank. It is an
> all-glass twin T-12 fixture with no modifications what so
> ever (yet). Being
> a "cheap" product, does anyone feel this kind of fixture
> would perform
> better with a cooling fan mounted on one end (or both) or
> should I assume
> that these were designed to cool themselves down to
> optimum temperatures?
> Also, does anyone use solar panels to run their fans? (I
> have a few extras
> and was thinking it could save me some time in avoiding
> the wiring...) After
> all there's plenty of light in that box.

With retrofits of fans, where the fan *can* fit usually
dictates where it goes.  That decision, along with open or
clsoed hood design might determine whether the fan sucks or
blows.

There are plenty of applications of fans in each type of
use, blowing and sucking.  E.g., Many small computers use,
and have for over twenty years, fans sucking air out of the
box.  Those boxes have thoughtfully placed inlet openings
so that air is drawn over the things that need it -- the
IBM ATs were designed this way.  Many newer computers, with
chips that run very hot, have small fans and heat sinks
mounted on them and blowing directly on the chips to focus
a high airflow directly.  These are in addition to the big
fan that might be sucking or blowing air into the box,
cooling the power supply, etc.  The point is, where is the
air going to flow.

Not having seen you hood, it's hard to tell which wind
direction would work best for you.  The archives reveal
folks that have used fans successfully in either direction.

The main thing to remember, if you use the fan to suck air
out of the box, is that the air into the box will tend to
come from the closest opening(s).  If you had a box that
was open underneath, and it say over an open tank, then
suction wouldn't move much air over the light bulbs at all.

Most tube-axial fans can be mounted in either direction.  
So if you try it one way and it doesn't work, you can turn
it around and try it the other way and just for the cost of
the time and effort it takes to remove and replace 4
screws.

Also note that there is a lot of variation in how effective
and how efficient fans of the same size are.

For some comparisons, check out this catalogue page from
Mouser Electronics:

http://www.mouser.com/index.cfm?handler=fra_pdfset&dir=612&pdffile=639

enter that all as one line in your browser -- you'll need
Adobe Acrobat to view the catalogue page.  The preceding
and the subsequent pages have even more fans.  The Mouser
web site lets you jump from one catalogue page to the next.
 Good prices too.


Good Luck,
Scott H.

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