how far should lights be from water surface?

[maui]

i'm setting up a new tank with some plants and lights, its a total DIY project I'm currently making a stand to hold my light fixture and i'm wondering how far should the lights be from the surface of the water?
my tanks also have glass lids - which i leave slightly open, are glass lids a problem when it comes to light? do they limit the amout out light that will reach the plants?
any help would be awesome - thanks in advance.

 

[Rubicon]

Depends on the kind of light. Flourescent (sp?) gives off little to no heat and can be within an inch of the water. Incandescent (sp?) lights give off tons of heat thus keep 'em far enough away to try to avoid cookin' the fishes So far's I know glass wouldn't stop the light at all unless its treated or tinted. Sunlight gets to my tank indirectly via about 3 or 4 panes of the stuff in a room with a large mirror and the plants grow like weeds even without the canopy light on, which it hardly ever is this time of year ( save for the late hours when nothings on TV and I feel like staring at the fishes for a bit ).

Unless you're buildin a tank big enough to swim in, in which case metal halide is probably the way to go but somehow I suspect we've not crossed that line. (yet)

 

[maui]

thanks for the info
ive set up my lights approx 5' from the surface of the water as they are on a diy fixture/stand that would be difficult to move for feeding/cleaning and such (i will post a pic as soon as i can). my tank is 12' deep so i think 17' from the light should be alright... or else ive got some major rethinking to do.
tank big enough to swim in eh.... interesting idea

 

[konrad05]

The lower the light the better for plants, there's a link somewhere on this forum where you put in your measurements and it tells you how many watts you need for low-medium-high light plants. With the glass lid, from experience, I would strongly advise that you design your canopy to be water proof because the glass WILL give you problems later on. I built a water proof canopy then added glass top just to keep things clean, few months down the road it kept getting dirty from the water evaporating and this would prevent light from coming in. I noticed a difference as soon as I removed them. HTH.