I think that the metal case should conduct enough heat to keep the ballast cool.

Oh, I don't worry about the housing and the reflector. I just don't want to overheat the glass.

If the thing is facing downwards the heat will rise away from the glass.

Well if I use it upside down it won't...

Do the glass panels have any etching about the thermal rating? I'd think the glass would be fine. How thick is it.

The glass lens must be tempered to handle the heat, even when the fixtures are mounted normally (base up). So, inverting the fixture and about doubling the heat on the glass should be no problem. Tempered glass can withstand a 1500w MH in a sports flood, so you should be fine

@Solanaceae : I don't know how thick the glass is but it is factory installed in the reflector. I'll see if I can determine that the next time I visit the salvage yard.

@BlueHalide : That is what I thought, but I want to be sure before trying anything.

Next time you go to the yard try to make out any model numbers on the fixtures. Look them up and you may be able to look the glass up with the fixture data that you find. Then you can determine whether it's safe to mount them like that.

My Widelight 450W PS MH High bay lights have a glass lens on them-have run them "upside down" now for few years without problems.The glass really doesn't get that hot.The fixure rating says it will handle up to a 1000W lamp.I would think if I was using a 1Kw MH bulb-the lens would get possibly too hot.At the surplus sale where I bought the lights they did have some 1Kw ones.Didn't buy any of those-probably should have bought one.Sometimes these lights show up in sales listed in the local want ad magazine-contractors selling older lights they replaced.

How about any gaskets around the edge of the glass ?

The glass is set in a bead of caulking and also has metal tabs that hold it there. It was made that way at the factory. I'll have a better look next time I'm there.

Since these would be used up side down, would it be best to use a different lamp than a standard universal burn M59 ? That's what's in there now.

I think it'd be fine, just relamp it before putting it to use.

Would a standard M59 universal position lamp be fine or should I find a specific type ?

I don't know. I don't know the quality of MH lamps between manufacturers, so Just go with your gut.

Universal is universsal no ? Whats the problem ?