led spacing

If you can get a 6" x 9" space then 12 LEDs would be fine, otherwise you're probably only going to be able to cram 6-8 LEDs in there (from what I recall the opening is pretty small on the Fluval Edge tanks). Each star pcb is just under 1" in diameter, and as evolved mentioned you don't want to cram them too close together due to heat. If you do "cram" them in make sure you run a fan on the heatsink for extra cooling.

Also, I'm not exactly sure what a cold finger is but you'll definitely want to put the LEDs on some aluminum to ensure cooling.

 

I have use Aquarium light bar for my tank .
It is good. and easy to assembly.

 

Thanks, I am thinking I will just go with 6 to start. I think I want to stick with the stock look. Definitely not much room though. If I feel more is needed latter, maybe I will modify it some.

A cold finger, in this case would just be a flat metal extension away from the heatsink to which some extra leds would be attached. I was thinking for height, it would bu ugly to have a big heatsink sticking out of the hood. The The leds under the hood would be attached to the heatsink directly and the ones outside of the hood to the cold-finger, which is also attached to the heatsink. I decided against this though, for now.