Help with LED spacing

[JohnsonSBK]

thinking about doing a DIY LED set up. im trying to figure out what the spacing would need to be for a fixture. my tank is 48"x30" is it better to space them evenly across the tank or do clusters?

[jimnrose]

I have a 72 x 24 (125g) and put them in 5 rows and offset (staggered) the rows. I didn't use a conventional heat sink but instead used aluminum u channel (1.5" x 1.5"). Jim

[der_wille_zur_macht]

Clusters vs. even spacing will really depend on your needs. If you want even light, space them evenly. If you have "islands" of live rock you want to illuminate, then cluster them around those islands. And so on. In this manner, LEDs give us a little more flexibility than we're used to.

[huskysglare1]

What's a normal spacing? 1.5" radius from the center of the LED?

[der_wille_zur_macht]

Honestly I don't like to concentrate on spacing. Instead, figure the number of LEDs you need to get the intensity and coverage you want, then figure a heatsink arrangement that'll get you within several inches of each side of the tank, then just space the LEDs evenly across the heatsink.

For example, on a typical 75g aquarium, you have 864 square inches of surface area (18" x 48"). You might end up with 48 LEDs. That's 18 square inches per LED, which is fairly typical. If you had two heatsinks that were 12" wide by 18" long, you'd be able to "cover" most of the tank with heatsink area (if that makes sense). Then, you'd just space out 24 LEDs evenly on the surface of each heatsink. If you did 4 rows of 6 LEDs on each heatsink, you'd end up with 3" between rows, and 3" between columns (roughly, depending on how far in from the edge of the heatsink you started the LEDs.) This would be a very typical build, and result in a typical spread of LEDs.

However, that doesn't mean all builds will end up with 3" spacing! If you try to use spacing to determine the number of LEDs you need for a tank, it's hard to take into account things like the percentage of the tank surface area that's not covered by heatsinks, or the ratio of "edge space" to "center space", etc. - which can all ultimately impact spacing for equivalent numbers/intensities of LEDs on different tanks.