Cooling T5's - fan placement

[GreenUku]

I'm planning to build a hanging light fixture for six 36" T5 lamps. I'm starting out overdriving two of the lamps (IceCap 430), but may overdrive more in the future.

Where would be the best place to place fans? It looks like some of the commercial fixtures I've seen blow air across the bulbs and some seem to blow air across the ballasts.

Thanks.

 

[GSMguy]

cool the bulbs

 

[Ti]

across the bulbs

 

[GreenUku]

Thanks for the replies.

Looking into this a little bit more, it looks like the fixtures I've seen that have fans by the ballasts are actually supposed to be pulling air across the bulbs.

This page shows two fixtures: one ATI and one Fauna Marin (sorry the page is in German).

http://www.tropicsea.de/berichte/solarisvssunpower.html

Supposedly there are little holes above the reflectors. The fans on top of the ballast area pulls the air across the bulbs to cool them and pushes it out the top. You can't actually see that in the pictures though...