DIY LED help

[makana]

I'm having a hard time understanding how to decide the number of LEDs needed for a diy fixture. There are lots of formulas floating around for it but it seems most people end up dimming their fixtures way down around 50% which leads me to believe they could have gotten away with less LEDs.

From what I gather the formula for figuring out the light spread is tan(degrees)*distance. When I do the math the diameter of the beam is huge even with 80 degree optics. I found an online calculator that says with 80 degree optics the beam is 13.43" only 8" from the bulb and 33.6 at 20". Does that seem correct?

[The Grizz]

In theroy you are correct but the further away from the source of the light the weaker it's intensity. In order to get good intensity out of any led you want the beams to overlap this also helps blend the colors more even.

So the taller the tank the more LEDs are required is my opinion to get a good intensity.

[makana]

So if that is accurate then two LEDs with 80 degree optics already covers more area than needed as far as distribution. So then how do I figure out how many are needed for intensity?

Why is the LED spacing recommendation 2"? If the spread is that wide I'm not sure why there is even any need to spread them out at all.

[The Grizz]

Not sure how it's calculated but I think Martin @ Modular LED has a way to calculate it.

If you look at a SOL fixture they have 8 pods of 3 LEDs each ( 1 - white, 1 - blue & 1 - royal blue ea. ) & each sol is sufficient for 24" x 24" roughly. If you look at my DIY build you can see what Martin & I came up with for my 8'er. Each heat sink covers 4' obviously & it's reccomended to have 6" difference on all 4 side between tank & heat sink.

Oh and just for reference I built my LEDs to suit my up coming 300 gal 8'er ( 96" x 24" x 30" )

[makana]

Well the two things I'm struggling with is the intensity and distribution of the LEDs. The AI nano is quite small and almost seems to be a spotlight. I could go the PAR38 route but they always look like spotlights. So I want to distribute the LEDs over a large enough area to not have spotlighting.

The intensity issue is less important. I will go dimmable so I could always just turn it down. At the same time I don't want to end up like others have where I can never turn up the light beyond 50% without cooking the corals.

[The Grizz]

What size of a tank are you putting them over? Where are you getting your LEDs from? I know that both Modular & Rapid LED have reccomended amount of LEDs for the size of your tank. It helps take a lot of the guess work out of a DIY build.

[makana]

I had been looking at Rapid LED. I guess I will just use their formula. I was just hoping to gain some understanding on where the formula comes from and if it is accurate.

The tank I was planning for is a 20 high. The other issue I had was the size of the heat sink. I was thinking of going big so that I can distribute the light evenly but most of the lights you can buy are smaller so the light is mainly focused over the centre of the tank.

[The Grizz]

I will be talking with Martin tomorrow and see if he can shed some light on the subject for both of us as far as number of LEDS.

As far as your heat sink personally I would make it 12" shorter & 12" narrower then your tank. Anything bigger you will be shooting light past the edges of your tank which would be a waist.

[makana]

Thanks alot. Let me know what he says.

The tank is only 24x12. So do you think it would work if I made it like a strip light? I could go 12" long and an inch or two wide. If that would work I could probably fit it in the old freshwater light.

I was thinking that I needed to make the heat sink only a little bit smaller than the tank to get proper coverage.

[pinhead]

There is an excel spreadsheet that does all the calculations for you. Type in your dimensions and it tells you number of LEDs, colour combinations and even cost of Crees at todays prices. I just checked and prices were updated today January 15th


http://www.nano-reef.com/topic/30415...emi-regularly/