Wow

[LoneStar]

No need to wonder about it. Physics has already figured it out. It's called the inverse square law. A simple way to look at it for what we care about is...

(far distance/near distance) squared = brightness

So for Mike... (18 / 4) squared = 20.25. So by lowering the lights to 4 inches from 18 you increased the light intensity at the water surface by 20.25 times.

Thats why you should stay in school kids

[erikharrison]

Thats why you should stay in school kids

Richard thanks so much for that information, now I am going to run around my house, lower my lights to 4" above my head run that equation on every light replaced, and I will report back in a diligent well-written DIY!! :P

[RayAllen]

Elementary my Dear Watson, elementary,lol. This is really interesting, but ive always run my lights 4-5" from the waters surface, with that said ive never run MH only Pc and VHO. Very Cool thread

[Bill S]

Richard -

Well sort of. Your math assumes that the bulb is an open bulb with no reflector - and no surrounding walls (white or otherwise) to reflect the light.

If you have an enclosed canopy, you will only lose light these ways:

Thru the side of your tank (put mirrors on your tank!)

From radiation heating - basicially, the heating of the surrounding items (walls, reflector, water, rock, fish) by ineffecient reflection of the light (that's why the sun makes you warm - skin doesn't reflect well...).

[hobogato]

dont forget that that equation is for a light sorce that is a point, not a long tube. i remember reading somewhere that long flourescent tubes dont follow that rule exactly because they are not a point light source like a metal halide.

[Richard]

A simple way to look at it

I did say that.

What I hated about physics was that the laws are pretty simple but then you get the test and had to do 5 pages of calculations just to get to the point where you could apply the law. Make one mistake along the way and you fail the test. Still the laws of physics always apply (even in maast land LOL).

Reflect light off of a mirror and the mirror becomes a light source and you can apply the inverse square law to it. I'm pretty sure a flourescent tube is made up of a bunch of points.

Point is...lowering your lights can make a dramatic difference.

[caferacermike]

So in the end I got it right the first time by running my lights 6" above the water?

[apedroza]

I feel like I'm back in physics class!!!!!!

[RayAllen]

huh, lol.....