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I would like to get a new light strip for my 3 ft tank, however the inexpensive ballasts are all 4 ft long.

How much light would I lose if I hung the ballast a few inches above the tank, over a glass top?

John,

Light intensity is inversely proportional to the square of the distance from the source. In English, light intensity in a tank that is 18 inches deep would be 44% as strong at the substrate level as the light as its source. If you raised the light 6 inches, the light at the substrate level would be just 25% of the light at the source or a decrease of 19% for the 6 inches in height.

__________
"To steal ideas from one person is plagiarism; to steal from many is research."
researched from Steven Wright

So I would need to produce 4wpg of light in order to have 1wpg in the tank?

I think that is right. its like the sun, really the nearer you are to the sun hotter/lighter it is. so the nearer the light is to the tank the more intense the light is.

this is going to sound ridiclous but i am really pleased i just worked that out - with the sun i mean. i am not normally so scientific.

hmmm. i hope that is right. i mean it makes sense right?



_______________________________________
Never be bullied into silence. Never allow yourself to be made a victim. Accept no one's definition of your life; define yourself.
Harvey S. Firestone

Okay, this purely polemical, but I think you're partly wrong, goldfishgeek.

Not about the light, you're right about that (I think), but about the heat. Theoretically, the heat on our planet is produced when the rays of the sun hit the earth's surface. Few kilometres higher than the surface, it will get be colder. Outside the earth's atmosphere it should be much colder than within the atmosphere. Somewhere in space, as you travel towards the sun you will start feeling the heat radiated by the sun itself but for anything in between, you'll be warmer somewhere in Scotland than in space.

Warning: getting too close to the sun could be dangerous and might result in severe burns. Please don't try this at home.

P.S., Moderators: I know this has nothing to do with fish and fishkeeping, but I couldn't help myself. Please feel free to reset my post counter.

Last edited by untitled at 17-Mar-2005 15:49

John,

If you place lamps with 4 wpg at the top of your tank, light intensity at the substrate level will be 44% of light intensity at the water surface. It is still considered to be 4 wpg for a planted tank with a depth of 18 to 20 inches.

If you suspend that same fixture six inches above your tank, then the light intensity decreases. Generally more intense lamps are suspended above an aquarium to minimize heat transfer to the aquarium. It is much more econmical to suspend high intensity lamps with HOT bulbs than to purchase and run a chiller for the aquarium.

__________
"To steal ideas from one person is plagiarism; to steal from many is research."
researched from Steven Wright

Right now I have some crypts that are doing fine with a 20w bulb over a 33g tank. However, I think it would still be better to hang 2 x 40w bulbs 6" above the tank.

Does that sound right?

Thanks Bob.