Distance between the lights and water

[Turtle77]

How far above the surface of the water should I mount my lights?

[DMBillies]

What kind of lights?

A general answer to this question is... as close as you can safely get them while still allowing yourself access to the tank (which depends a lot on the type of lights and how your hood is designed).

[poolkeeper1]

You also need to consider how much heat will be transferred to your tank so you don't fry everything.

[Turtle77]

1 250watt Metal Halide and 2x 75watt Actinic in a plain retro kit, no hood, no canopy. So I am either going to have to hang this ugly thing from the ceiling which is unacceptable to me because it is an eyesore, or I am going to try and put something on the top and hide it. So I am trying to figure out how to get it up there and how far away to put it from the water and put a fan up there between the lights and water. brainstorming ideas. opinions are welcome :-)
Here are the lights
<a href="http://www.flickr.com/photos/11107081@N02/2602195961/" title="P6220050 by chernalp, on Flickr"><img src="http://farm4.static.flickr.com/3062/2602195961_77debe26c9_b.jpg" width="1024" height="768" alt="P6220050" /></a>

here is my stand , this is an old picture before I cleaned it up and painted it. As you can see its all one peice, no canopy for lights, no hood action or doors or anything like that.
<a href="http://www.flickr.com/photos/11107081@N02/2599431304/" title="P6200006 by chernalp, on Flickr"><img src="http://farm4.static.flickr.com/3234/2599431304_4889b43d55_b.jpg" width="768" height="1024" alt="P6200006" /></a>

[gflat65]

I always hold my MH about 8" off the water, when I can, to help with heat and still allow access into the tank. You don't lose much light by raising, but you allow it to spread a lot more (reducing localized intensity in the tank). Water is the big light killing medium. Think about it in terms of the sun. Its' light travels a long distance but the reduction in intensity from the edge of the atmosphere to the water surface is small compared to how fast it loses intensity in water depth.