Join Date: Jun 2013
Location: Gilbert, Arizona
You're at a point where either option would fulfill your needs perfectly. Choose the one that looks better. Its true that with the thinner U channel the fixture as a whole will stay slightly cooler than the 1/4" flat, but the LED junction temprature will not be significantly cooler with either.
I would go with the flat just because IMO, it's easier to make look good. On my light, using 14 3w cree's I actually used a 1/32" pattern mesh and its staying room temp (about 82F) perfectly with no active cooling.
What I'm seeing with most aquarium LED fixtures is really excessive cooling. Unless you're actively keeping the leds a fair amount below room temp (peltier or chilled substance cooling, etc) there won't be any noticeable difference in the lifetime of the diode, and using systems like that removes the space benefits and cost savings of LED!