Originally Posted by FrenchFry
If there are 5 LEDs per row spaced four inches apart, then the three rows would be centered over the middle 20 inches of a 30 inch tank. With 40 degree optics, wouldn't that mean the ends of the tank would be quite dark?
The ends of the tank would not be as bright as the middle, but they wouldn't be dark. You could increase the number to 6 per row and brighten up the ends a bit. Remember, light will reflect off the end glass to increase the brightness near the ends, too. 18 total LEDs will be a bit easier to fit to a couple of LED drivers too.
If you want to use 60 degree optics you will have to either move the light closer to the tank or switch to Cree XP-G LEDs.