heatsink size?

hey im debating between two heatsink options for 36 leds on a 40 breeder....

10" x 30"
or
8.5" x 30"

with the 10" i can have 4 rows of 9 leds but with the 8.5" i can have 3 by 12 leds. what do you think is best?

 

that depends on what kind of LED's, wattage, thickness of the alum base and height of the fins if any on the heatsink.

I have built LED's, one watt, on a heatsink with no fins and 1/8 inch thick, LED's approx one inch apart, 60 total lights, continual fans cooling it.

I have also built a cree, 6 LED, 3 watt each, lights one inch apart (center to center) on a heatsink with a 3/16th base and one inch tall fins, measuring 3 inches by 3 inches, continual single fan cooling.

It sounds like you are spreading them apart a ways, which is fine, a pendant 8.5 x 30 would look nicer than a more square one, plus you can spread the light out wider to cover more length of the tank...

 

well its gonna be 3w cree xr-e's and 1" high fins. i want to keep it as one single heatsink, not too bulky but as the same time have enough spread for a 40 breeder.

 

for comparison, I have a 5 inch by 11 inch 120 watt led fixture over a 40 cube, 24x24 and had to raise it up about 12 inches over the water to get the coverage, it has no lenses and its 120degree spread covers front to back just fine but the sides spill over onto the floor.

If you have lenses on your light, you may have to raise it up to get the coverage is all. I like the looks of long narrow fixtures for rectangular shaped tanks and would go with a fixture that has that same look.

Both your heatsinks are the same length so I'm hot sure you will notice any spread differences with the 1.5 inch width difference since the LED's will be a bit closer with 3 rows at 30 inches rather than 4 rows in the same length, isn't a 40 breeder 36 inches long by about 16 deep? If you are running lenses in the fixture you may have coverage issues with the narrower heatsink and be forced to go with the wider one.

 

any other oppions?

 

bump

 

What optics and how high above the surface do you want to hang/mount the fixture?

 

i would go with around 50-65deg optics, and i would hang it around 6"-8"high

 

Wider is better, in that case.

 

ok thanks but one more question, how do you think i should wire 36 leds (18 white - 18 blue) so that i can control whites and blues?