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[APD] Re: DIY Metal Halide Fixture

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

For the metal strip, use a material that is a poor(er) conductor of heat than aluminum. Also, use a thin piece and bend it such that there is a long amount of bracket material between the reflector and the mounting surface. This will minimize the amount of heat transmitted *through the bracket*, but radiated heat from the bulb will still heat the wood if there is little separation between the two. For the bracket, I'd use a piece of mild steel sheet, maybe 1/16" thick or maybe a little less. You can get this from Lowes in their hardware section.

For the water shield, use glass -- tempered would be best in this application. Glass won't deform or melt from the heat, and the tempered glass will have better resistance to shattering if you do get water on it while it's hot.

Also, make sure you have at least an inch or two all the way around the reflector to allow for good airflow. If you already have the maximum spacing around the assembly in your hood and the temperature is still higher than you'd like, try mounting a small fan in the hood to exhaust the hot air. Make sure there is good ventilation both in AND out of your hood to allow air to circulate and help keep the internal temperature down. If you use a fan, position it so that it will generate maximum air flow around the area of the reflector, possibly positioning one fan near each reflector assembly. You don't need much fan power for this, a little air movement will go a long way since you only need to remove a relatively small volume of high temperature air to make a big difference.


***************************** Waveform Technology UNIX Systems Administrator

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