How much heat transfer from light?

[Louis Governo]

I know there are a ton of variables, but that aside, can anyone give me an idea or opinion of tank temperature increase by running the following lights?
36 x 18 x 25 tank
ambient temp around 75 with 6 T5 39 watt bulbs 6 inches above the water line.
With 8 bulbs?
Ignoring all other sources of heat and no fan across the surface of the water.
Thanks

 

[The Grim Reefer]

All things being equal running 8 vs 6 T5's shouldn't make a difference. If you have the fixture sitting right on the tank then the added size of the bigger fixture will trap more heat and lead to some sort of temp increase but it is hard to say how much.

 

[Louis Governo]

I shouldn't have put both questions together. Any guess on how much the temp would rise with either fixture? From 75 to 79? or maybe 80? Since I've never used them I have no idea.

 

[The Grim Reefer]

As long as there is a gap allowing for heat to escape the tank I would say 79 degrees is a good bet. You should have the light 4" above the water anyway so it should allow plenty of air circulation so heat build up shouldn't be an issue. .

 

[125G Reefer]

I agree. ^^

 

[Louis Governo]

Thank you. At least I have an idea now.