Magic - how do you find the U channel works as a heatsink? Does it keep them cool enough? And how many do you have attatched to each channel?
Before building mine I had a discussion with Dave at Reeflections Aquarium in Melbourne who built all of the LED lights for the shop tanks. Initially he used the standard finned heatsinks but soon realised that these were overkill for his situation and reverted to using aluminium channel. From memory, the channel he used was smaller than me but he had his LED's spaced a fair way apart.
In my situation, the channel is a relatively cheap alternative. I am currently driving them at 850ma because they are located a bit higher than their final location and they get warm, but not too warm to touch. I plan on reducing them to 750ma when I finish my new hood which will reduce the heat ouput further.
I mentioned my situation -I live in Hobart so our summers are not generally extremely hot; my tank is in a relatively cool part of the house; we have a reverse cycle air conditioner in the room which we use when it does get hot. Your situation may be different ;)
I currently have 9, 19, 20 and 12 led's on the 4 channels which are all 1200mm long.
:)