# How Hot Do MH Bulbs Get?



## AaronT (Apr 26, 2004)

The reason I am wondering is because I am in the process of building a DIY MH/T8 lighting fixture and would like to know if wood would be a suitable material to use for building the pendant shell. My fear is that it is flammable and could start a fire if it got too hot. Other options I can think of are aluminum or acrylic, both of which would be a pain to work with and the acrylic might melt. Any suggestions?


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## Praxx42 (Mar 4, 2005)

Hmn. What's the wattage of the MH bulb/s? I ask because two 400W MH bulbs raised the average temperature of a 9'x10' room by more than 15 degrees every day I had them on.

I do'nt know if they'd be hot enough to smolder a wood frame, but they will certain burn the $#!+ out of you if you touch a lit bulb. Take my word for it.


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## titan97 (Feb 14, 2005)

The MH bulbs I have here at work get very hot. As for actual temps, I am not sure. They are 400W bulbs in aluminum enclosures. I would avoid the wood at all costs. I would imagine that the MH bulbs would get hot enough to burn the wood. Not to mention that the wood would become very cracked and dry over time.
As for acrylic, you can't use just regular ol' acrylic. AFAIK, Most MH fixtures us a UV-resistant/UV-shielding acyclic that won't discolor or degrade with the intense UV put off by a MH bulb. 
Wouldn't you want a reflector anyway? 

-Dustin


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## glenhead (Jan 29, 2005)

Temperatures at the lower edge of 400W pendant fixtures are listed several places at 100ºF above ambient - so call it 180ºF degrees *at the lower edge* - so you can guess what it probably is on the top surface of the bulb. I know the halogen bulbs they put in those floor lamps are stated to run at about 350ºF - that's why they'll set the drapes on fire if they come in contact. I don't know the relative efficiency of a metal halide compared to a halogen or incandescent bulb, but I'd give odds it's not much more efficient. Wattage is also an indication of heat output - if a 100 watt incandescent bulb gets as hot as it does, quadruple the temperature and you'll have a good guess. There are thermal insulation materials (used in automobile firewalls) that are rated to over 450º, something like that would probably provide sufficient protection to make a well-ventilated wood enclosure safe.


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## gnatster (Mar 6, 2004)

A few things to design into a wooden MH Canopy. 

Fans, you want to draw air through the canopy, keeping a good flow of air will keep internal temps down. 

Air gap between the reflector and the top. When you mount the reflector it should stand off the top of the canopy some to allow airflow over the top,this cuts down on convection heating. 

I've seen some folks go as far as adding some moisture resistant automotive firewall type backing between the reflector and the top, also keeping an air gap.


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## AaronT (Apr 26, 2004)

Thanks for the replies. I'm only using 175 watt bulbs, though I'm sure they'll get plenty hot as it is.

I suppose I wasn't very descriptive in my original post. I will be using an aluminum reflector and am incorporating the suggested airspace into my design. The bulbs are mogul based, not the DE HQI's, so UV should not be a problem. It is my understanding that the single-ended bulbs have UV protective jackets on them. Either way I will be using a glass shield to prevent bulbs from breaking due to contact with myself or water.


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