DIY LED Light Questions

[Ron99]

Originally Posted by Beanz

Ok, do you think that if i just get the 36 LEDs and raise the fixture up, 4 inches like Cal said (maybe higher if spotlightinf still occurs, or would this reduce PAR too much?), this would eliminate the spotlighting and work for keeping SPS closer to the light and LPS and maybe some softies near the bottom of the tank?

Thanks, Ian

I would say no. The reason for more LEDs is not only for even coverage and colour blending but because the overlapping output of the multiple emitters adds up to the amount of PAR you want. I did a quick experiment measuring PAR output of single emitters driven at 350mA at a distance of about 3 inches from the LED and no optics. A cool white Cree XRE put out about 176 PAR, a SemiLed cool white (about a middle of the road bin, not the highest brightness bin) put out about 100 PAR and a cheap generic chinese white LED put out about 50 PAR.

So even with say a 60 degree optic you will probably have no more then 350 PAR at 3 inches from a single emitter. You need the light from the LEDs to overlap to add up to the PAR you want if you want to get up to 500 PAR for SPS.

For further comparison, a 12" AI module uses 24 Cree XPG and XPE emitters to give the high PAR numbers it produces. You would need 3 to 4 modules to cover a 48" tank so that would be 72 to 96 LEDs.

Unfortunately, if you want a high output LED fixture there are no shortcuts and the up front costs are relatively high. But you will save in the long term by not having to change bulbs for 6 to 8 years, using less electricity, and putting less heat into your tank so you may not have to run a chiller or fans etc. (my tank stays between 78.5 and 80 degrees depending on the ambient temperature. During the heatwave it went as high as 81.5).

[Ron99]

Forgot to address the drivers. You could go with the non dimming drivers as you suggest but as Steve says you won't be able to do nice sunrise and sunset effects or adjust colour temperature or change things for acclimation purposes. If you don't care about that and just want to have the blues come on at a set time and then the whites come on at a set time you could save a bit by using non dimming drivers for both. But the cost difference for dimming drivers isn't that much more and gives you more flexibility for the future.