Too Much Light?

[jjwill_sdsu]

So I'm considering purchasing a 48" Current Sunpod MH fixture for my 72 gallon bowfront. The fixture would sit on the tank with the included leg stands. I was originally going to go with the 2x150W version with lunar lights, but I found a good deal in a classified for a used 2x250W. My only concern is if the 2x250W is just too much for my tank heat- and light-wise. I don't have a chiller and don't intend to buy one, so heat could be an issue. I do keep my house at about 70 degrees and have a heater to keep the tank around 78 at night with the lights off. I would like to get into more light-hungry corals/clams, but I also want to be able to keep some softies and mushrooms without frying them. Any thoughts if the 2x250W will work in my setup? Thanks.

 

[reefraff]

Should be fine light wise. Heat may or may not be an issue. If you have a sump you can always run a fan across the water to help keep the temp down.

 

[jjwill_sdsu]

If my sump/refugium is open top, should that allow for enough evaporation to compensate for the extra heat, or am I going to have to take the glass top off of my tank?
On a related question, is the heat production per watt actually different between power compacts and metal halides? i.e. If you have 500 W of power compact (a lot harder to fit in one place I know, but hypothetically...) vs. 500 W of MH, do they produce the same amount of heat? I just didn't know if people usually said that MH's were hotter because you typically get a lot more watts for you buck or if there was a fundamental difference in how the power consumption was split between light and heat production.