I've been doing a lot of research in choosing my own LEDs so I can hit a few points there.
In regards to lens angle, it's the angle of the reflectors mounted around the individual LEDs. A 90° means the light is focused 45° downward on each side... an easy way to think of this is like this, that makes a right triangle, so for every inch down from the light to your tank bottom is one inch out the beam goes in each direction. With 90[FONT=arial, sans-serif]° optics if your light is 18" up, the light goes 18" out from the center.... however that's for EACH LED not the whole unit. it's not a single source of light like an MH bulb or a Kessel (and as such, does NOT create the shimmer like those units do), so you have overlapping patterns created by each reflector on each LED. That is, in our example the light may be going out 18" from each edge, but only the outermost LEDs reach that far. since the unit is 15"x8", you have to subtract the length and width from the edges to determine the area of full coverage. at 18" from the floor, the area of full coverage is about 21"x28"
90[/FONT]° is great general purpose, if you have a shallow tank like me you'll want 120°, that means each bulb goes 60° in each direction so you get an approximately 30" radius (per LED), and it (of course) doesn't penetrate as deep as 90[FONT=arial, sans-serif]°. So at the same height as the last example, 18" your coverage area is roughly 45"x 52" thought it's probably less than a third as bright at that depth. 60[/FONT]° optics are best only used in tall tanks.
[FONT=arial, sans-serif]Please don't think I've got it all figured out, this is just a little math and the culmination of some reading on the internet. I'm still looking for good advice myself. I will tell you, call Reef Radiance, I called a few weeks ago and spoke to Rick and learned more in 15 minutes than in a week of reading.
My frag tanks are 72x18 in footprint and 12" deep and i'm putting two of the Reef Radiance Lumentek 180s with 120 optics on those... hopefully next month.
You might want to take a look at the Lumentek units, they're more of course, but when you consider that you'll need three dm-155e units, and timers, add all that up and a couple of the Lumenteks (don't know if you'd need the 180s or 240s) wouldn't be much more with a better featureset, that was the conclusion I came to. Just food for thought.
Russ[/FONT]
