Re: [APD] DIY Metal Halide Fixture

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

Remember that MHs do not put out more heat wat for watt
than a fluorsecent bulb -- it's just concentrated in a
smaller area. So the key is spread out the heat and carry
it away from the wood.

If it was me then I would:

Use glass for shielding instead of plastic this is an
excellent example of when glass is much better than
acrylics.

Use a larger piece of metal for the bracket so that it will
disperse the heat energy over a greater mass and large
volume. However, if the metal is very short (i.e., the bulb
is very clos to the wood), then the wood will be getting
about as hot as the metal even without the bracket
attached. So, I would space the reflector away from the
wood and provide plenty of ventilation on both surfaces of
the reflector. If you are using a fan, have some of the air
flow over the top of the reflector between the reflector
and the hood.

Also, you can get a ceramic pad (they used to make them out
of asbestos but not any more) that plumbers use to protect
wood in the house walls when they are using a propane torch
to sweat copper pipe fittings. These are usually about
8-12" square and you can find them at Home Depot and
similar joints. Affix the pad to the wood (with some screws
that are too short to go all the way through the wood)
directly over the bulb location. This will help retard the
passage of energy into the wood faster than the wood can
shed the energy -- but ventilation will still be required
for this insulation to help much.

I think the flash point for most woods is a tad more than
600F. The outer bulb surface temperature is possibly not
more than about 350F and very likely less than 500F. Still,
if too much heat is located in too small an area, you will
dry and age the wood prematurely.

If you get an inch or so away from the bulb and provide
some ventilation, the wood should not reach an unreasonably
high temprature.  However, I believe the finish on the wood
will probably prematurely age if the temperature of the
finish is much more than about 150F-180F, depending on the
finish.

Hope that helps,
Scott H.

--- Shalom Levytam <shalominc at yahoo_com> wrote:

> Hello,
> 
> I have finally gotten a chance to complete the
> lighting for my tank; however, I have run into some
> problems which I am hoping someone could help with.
> 
> The setup is currently an aluminum reflector that
> almost looks like a roof with the middle portion flat
> and the sides at 45degrees down.   The socket is
> mounted sideways within the reflector.  A metal strip
> attaches to the top of the reflector and is used to
> mount the reflector to the wooden canopy.  Finally, a
> piece of acrylic is used as a water shield for the
> reflector.
> 
> Two big problems!  First, the metal strip mounting the
> reflector gets TOO hot!  I am worried that it might
> catch the wood on fire by some misfortune.  Second,
> the acrylic sheets I used as a watershield have
> started to melt.  I only had the light running for 30
> minutes.  
> 
> Does anyone have a suggestion as to better materials
> or methods.  The lights are mounting really close 2-3
> inches from the water so I think i need a watershield.
> 
> Thanks,
> 
> Shalom
> 
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=====
--- Christel Kassellman is returning to America! ---
The Northeast Council of Aquarium Societies will feature Christel, author of _Aquarium Plants_, among its speakers at its 30th Annual Convention. It's the longest running consecutive general tropical fish convention in the country and one of the most fun to attend. 

March 18-20, 2005
Marriott Hotel, Farmington, CT
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