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View Full Version : 400w light fixture mounting!!?!?!?


THP
12/06/2007, 06:11 AM
I've got 3 luminarc III reflectors that I have mounted to a 2x4 running across the top of a tank. The reflectors will be running 400w lights and I'm worried about the heat on the 2x4.

What is everyone doing to avoid heat/fire!?!?

I was trying to avoid hanging via wire but would a 3" bolt running through the reflector and through the 2x4 work to disapate the heat from the 2x4? I have room to space the reflector about 3/4" from the 2x4 max. I want to keep the reflector away from the water by at least 9".

JaredWaites
12/06/2007, 09:10 AM
Well I think with an exhaust fan or another fan blowing across your lights would be enough to where you can mount it directly to the 2x4.

Think about the many people that have bulbs and VHO's directly in their canopies, sure they experience heat build up, but no fires.

THP
12/06/2007, 09:20 AM
True, and maybe I am being too cautious. I wish I still had my 250 setup lying around so that I could see how hot that was getting.

The intention is to have fans but I guess my fear is coming from the fact that these are 400w lights and the 2x4 was getting quite warm even with the automotive heat shielding I put between the reflector and 2x4

Also, what if the fan(s) ever failed?

formanbob
12/06/2007, 03:07 PM
In order to make wood burn, you need to raise its temperature to a critical point. How hot? Well, at about 390 degrees Fahrenheit, wood dries out, and a slow pyrolsis takes place (the wood breaks down due to heat, but does not burn per se).

Between 390° F and 530° F, a piece of wood is reduced to charcoal, but without flame.

Between 530° F and 930° F, wood will be ignited by an open flame.

At about 1000° F, spontaneous ignition occurs..




I think you are good...

THP
12/07/2007, 06:28 AM
<a href=showthread.php?s=&postid=11329181#post11329181 target=_blank>Originally posted</a> by formanbob
In order to make wood burn, you need to raise its temperature to a critical point. How hot? Well, at about 390 degrees Fahrenheit, wood dries out, and a slow pyrolsis takes place (the wood breaks down due to heat, but does not burn per se).

Between 390° F and 530° F, a piece of wood is reduced to charcoal, but without flame.

Between 530° F and 930° F, wood will be ignited by an open flame.

At about 1000° F, spontaneous ignition occurs..




I think you are good...

Thanks for the informative breakdown. I think I may be over cautious but since you seem to be quite knowledgable on this topic, would you know how hot a 400w MH bulb would get?

formanbob
12/07/2007, 06:47 AM
SE or DE..?
Is the first question.
I am assuming a SE
I had a 400w se and the surface of the bulb was around 200 but the inside ( the little glowing center) went from 380 to 440 at times, but 1 inch away was only like 160 180 and the outside of the reflector was no worse then a bare heating pad.

THP
12/07/2007, 07:00 AM
<a href=showthread.php?s=&postid=11333437#post11333437 target=_blank>Originally posted</a> by formanbob
SE or DE..?
Is the first question.
I am assuming a SE
I had a 400w se and the surface of the bulb was around 200 but the inside ( the little glowing center) went from 380 to 440 at times, but 1 inch away was only like 160 180 and the outside of the reflector was no worse then a bare heating pad.


hmm, heating pad? Well, mine are SE as you correctly assumed but touching the top of the reflector after 15 minutes of run time is enough to burn your skin. This is why I got worried. They are Luminarc III reflectors so perhaps that is the difference. The reflect light really well but since they are enclosed with the only venting at the bottom, I believe the heat build up is worse than a spider reflector or something like that.

formanbob
12/07/2007, 07:18 AM
Do this, you can get one of those IR thermometers for $20 these days, or just put an old aquarium thermometer on top of the reflector see what you get.
One thing I did before is use concrete backer board. It is great at isolating heat…

THP
12/07/2007, 07:27 AM
great, thank you. I will look into both your suggestions. Very much appreciated.