DIY MH lights .. How big should hood be?

[beattyr]

I am going to build my own MH lights and hood. How high from the water should I have the MH lights.
Lights will be 250w 6500k. Tank is 37gal. I want to put something on top of the tank vs hanging them from the ceiling.
Thanks
Rob

 

[jeo]

about 8" should be good, thats what I am going for on my canopy

 

[richard rendos]

All my lights are 6" from the water surface and canopies are 10" high. Most people recommend bulbs be 8" or higher from the water, but I like mine where they are.