LED Spacing?

So, trying to plan out my LED build... haven't found any concrete suggestions or guides to LED spacing... How far apart do i put these things to ensure a good even spread using 60* optics? I have a 75 gallon and i'm hoping to house them in the canopy which would only put them maybe 2-3" above the water (Yes i'll have a splash shield.) That said, is that a bad idea? i've seen a lot of builds with them hanging much higher even up to 4-5' above the tank!

 

It's not a "bad" idea, but with 60deg optics, you'll need to have them rather close together otherwise you'll get spotlighting. I'd say ~1.5" apart. And then you'll want to ensure you have good flow over the heatsink to adequately cool them packed so close together.

Personally, I like narrowish (60deg) optics mounted 16-20" off the tank surface.

You can do what you've got in mind, but you're going to spend a lot more on excess diodes to get a nice, even blend.

 

so, if i mounted 16 - 20" off the surface with 60* optics could i space 2-2.5" apart and still achieve a good amount of spread?

 

Correct. It's also a matter of how wide your heatsink is, vs. how wide your tank is.

 

it has also been suggested that i could run them this close to the water (2-3") without optics at all???

 

Depends on the depth of your tank.

So what's your tank dimensions?

 

typical 75 gallon ummm 48x18x21 sorry, thought i included that in the op.

 

as for the heatsink, planning on using c channel from HD. End up with 4 rows of LEDs with fans to help with the airflow... and cpu grad thermal compound to aid in heat transfer

 

So at that depth (21"), you really need optics to get decent penetration (PAR) near the bottom of the tank. 60deg are really your best option here. 80's might be an acceptable compromise, but you certainly need some optics if you desire to keep moderate to high light corals.

If it was me, assuming CREEs, I'd have ~48 diodes, using 60deg optics, on a 8" wide heat sink (and somewhere around 40" long), hung 12-15" off the surface.

If you really want them close to the surface, I'd probably use 80 deg optics, on a 10" wide heat sink. And you'll need 60-72 diodes, unless some spotlighting does not concern you. You WILL need dimmable drivers, as you likely won't be able to run this many diodes at more than 50% power without bleaching corals.

Regardless, I'd only consider dimmable drivers; there's a handful of circumstances where constant current are applicable; this is not one.

While I'm not a fan of this type of improvise, it can be done if you understand how heat sinks really work. Make sure you have a sufficient number of fins.