LED spacing for DIY fixture

so, im looking at DIY LED fixture for my tank, and have looked before several times, the one thing i always get stuck on is how far apart to space the LEDs. any of you people who already have done this have any pointers? I have seen everything from 1.5 to 4 inches.

 

depends a lot on the type of LEDs you are using
and the beam angle of the LED
They are available in 45, 60, 90 and 120 degree beam angle ( the spread of light)
the narrower the beam angle the closer you need the LEDS together to avoid dark areas and shadows

having beams from adjascent LEDS overlapping slightly gives a more even spread of light

Steve

 

I think that depends more on what type of coral you are looking to grow. More L.E.D's will make it possible to grow higher light corals and they will have to be spaced closer together to fit. Less L.E.D's won't give you as many coral options and will have to be spaced apart more to fill the area and light your whole tank.

 

So what leds are you using?
CREE XP-G for the white and XR-E royal blues?
or something different?

 

i was looking at the 3W cree white/royal blue LED's. Also im looking at something that will handle SPS, and be comparable to my current lighting (2x250MH +4 t5s). Im thinking i would need optics on the LED's to achieve the same levels of PAR i have now.

 

yeah optics no doubt... You can get away with 48 LEDs being run by 4 brightwell drivers and still have full coverage if you get some 30 or else 45 degree lens.

 

just going to have to raise them above your tank a few inches.

Dont know if you remember any trigonometry but the formula for calculating the diameter of the beam is this: tangent(place degree angle here)*distance of bulb
For example, if you have a 30 degree lens and you want to know the diameter at 20 inches: tan(30)*20in = 11.54in diameter

 

48 LED's hmm I guess i should read more. I was thinking i needed like 200.

 

if you go with the 3 watt CREE leds then you will not need that many. also, the CREE's have the highest lumen output for their wattage.

they just came out with a new bulb (the XM led) that wont be on sale until fall 2010. Their best bulb now is the XP-G with 116 lumens/watt, this new bulb has 160 lumens/watt! CREE really is the cutting edge of LED technology