distance of lights to gravel?

[CHINABOY1021]

If i'm planning for an open top tank, what's the maxium distance i can raise the lighting fixtures for still efficient lighting?

i remember someone posted before, but i cant find the thread. someone also said there's a rule of thumb stating certain wattage efficiency lost compared to heigh of the lights.

can someone clear this up for me please?

[Matak]

Watt kind of lighting are you using?

[CHINABOY1021]

oh oops.

I will be using normal fluorescents. 36 inch lengh. 4 x 30 watters. 2aquarium canopy fixtures.

i know metal halide is like the only way to do open-top. but its also super expensive plus i dont plan on having my lights above 1 foot over my water surface. can i still work with my normal fluorscents over my 45 gallon?