Led spacing questions

I have a 90 Gal tank standard dims ( 48 l x 18 w x 24 deep)

My fixture will be in a canopy so it is about 6.5" off the water and about 28" off the sand.

How far in from the edge should I start my LEDs and how far between each LED

If I did the math right with an 80 degree optic I would get the best light hitting the edge of the tank about 11 inches down from 6 inches in. Does that sound right?

I was thinking about 2" spacing as well.

Thanks in advance

 

From the edge depends how long your heatsink is. Just remember that the strongest part of the LED's light is in half of the total angle. So 40 degrees with your 80 degree optics.

If you are going full spectrum with various colors, I would cluster the LEDs. If you are just going blue/white, that spacing should be fine.

How many LEDs do you plan to get?

 

Guess more info would help, lol

I will have a total of 52 LEDS and my heatsink is 48" long running the length of my tank. IT is actually made up of 4 individual 2" channels that are spaced about an 1 1/2 inches apart.

As for make up it will be 24 RB , 8 NW and 4 WW as a base then adding 6 blue , 6 TV , and 4 Turq. So not really a full spectrum build but more than just RB/W

The 40 degrees is what I was working with (strongest light) If I remember my trig ( been a long time) tan (20)=6/Adj.

20 degrees would be the spread in one direction for the strongest light of an 80 degree optic, 6" horizontal in , adj would be the depth and calculates to about 11 inches deep when it travels the 6 inches to the glass

 

On my 125 I have (3) Evergrow/ReefBreeders 120W fixtures. All are about 6-7" off of the water. The LED's are about 8" away from the glass. I believe all have 90° optics. The edges are certainly more dim than directly over the LEDs, but not bad:

 

Your math was right. So one LED 28 inches from the sand with an 80 degree optic theoretically spreads the light in a cone with a radius of about 23 inches. The strongest of the light will be in the at that 11 inch radius you calculated. Of course this is not taking into account the light hitting the water's surface and the brightness of the LED.

But I would say it's safe to say that no matter you you place your LEDs on the heat sink, you will light the whole tank and most of the "strongest" light will hit your tank.

Since you are using colored LEDs, I would try to place those towards the middle of the heatsink and space them out accordingly. To make the color spread as even as possible, make sure the colored LEDs are surrounded by the blues/whites.

X X X
X X X
X X X

I would do 6 clusters of 9 LEDs like above. The spacing will depend on if you have a center brace and how you want to arrange the LEDs.

 

My heatsink is currently 4 lengths of channel , 2" wide and 1.5 inches apart.

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After all this calculation I am considering dropping 1 and moving them closer together to make the clusters closer together.

Now its time to start looking at layout. Thanks for the help

 

No problem. Check out Shin's LED build http://www.3reef.com/forums/led-aqu...ectrum-led-build-all-125835.html#.UnabmZT44so

Might give you some other spacing ideas.