Determining pendent height
I am hanging two 150W ADA Solar I's over this tank. The general rule is that 1 MH can spread about 24", but unfortunately I am right in the middle with the length of this tank. 2 lights might not be enough, but 3 will certainly be too much.
Before I build the light stand, I need to determine how high off the top of the tank I need to hang the lights. To do this, I held the pendent at different heights to see what kind of light spread I am going to get. You can see by these two pics that even 2 inches in height difference doesn't make that much of a difference lengthwise. Unfortunately, it does make a larger difference depthwise
Here are two pics of the experiment. The red dot marks the center and the blue dots are in 4" increments from the center.
10" height - about 12" of solid spread
12" height - about 15" of solid spread
I have determined I am going to start the lights at about 10" from the top of the tank and make the light stand a full 84" tall. I may lose full spread at the total top of the tank, but due to the depth of the tank I will sacrifice a little spread at the top for penetration to the bottom.