Holy smokes its bright in there!

[bprewit]

Well built a new hood today or atleast got it half way finished and set it on the tank. I lowered my MH and VHO bulbs a total of 3 inches lower to the top of the water and lined the top few inches of the sides with aluminum sheeting and man to my eyes the tank is almost twice as bright as it was before I made these changes. I am going to reduce the MH cycle time a bit as im afraid the sudden light increase may **** off the corals and increase it gradually over the next week. Never would have thought that lowering the lights by only 3" would make that big of a difference.

[christerrell2k3]

hmm good to know, im going to have to wait tell april for some MH's on my 65gal(36x18x28orsomthing)... and it has 2 glass braces about 4 inch from each side.... So i have to figure out from there....

How far were they from the water the first time?

[bprewit]

Inside of the canopy was just bare wood on the old hood. I actually didnt want to order a new reflector so I bought aluminum sheeting $5 for a 6"X10' roll. I took some extra fine buffing compound that I used for the car and actually got the sheeting to a near mirror like finish. Then it was easy enough to bend and attatch where I wanted it. I am guessing it was a combination of both that made it brighter- moving the lights closer to the water and the addition of the reflector.

christerrell2k3 -
The bottom of the MH bulb was 10.5" from the water surface the first time. I cut the old hood a inch at a time to lower it until I found the light coverage I was looking for and it is about 7" from the water surface now.

I ended up with two 48"VHO bulbs and one 250W MH bulb on my 55g. I have some LPS and softies in my tank so I was able to concentrate the MH over the middle of the tank and on each end it is a bit dimmer so I moved all the softies to the ends, LPS closer, and the SPS (only one at the moment) high right under the MH. This way I am hoping that I can keep the few corals I like and keep them all happy in a little 55g tank.

[Richard]

Good reflectors make a big difference. There is also the inverse square thing about light and distance. I'm no physicist but as I understand it it goes...

(far distance/near distance) squared = brightness

So for you... (10.5 / 7) squared = 2.25. So by lowering your lights 3 inches you increased the light at the water surface by 2.25 times.

[bprewit]

Wow thats a big difference! Thanks for explaining that to me as I really didnt quite understand.

[alexwolf]

So by lowering your lights 3 inches you increased the light at the water surface by 2.25 times.

that makes perfect sense!!!

The whole key here is "at waters surface"

[Richard]

Here's a more complicated look at how it works.
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/isql.html

Yeah, "at the waters surface" since that's the distance we know. You could do it for a coral though. If he had a coral that was 15" away before he lowered the light 3.5" then...(15/11.5)squared means that light at that coral is 1.3 times as intense.