LEDs over 20 long how high and optics?

Hey guys. I have some questions about hanging height and optics.

I have 24 leds on a 6x10 heatsink I'm going to hang over a 20 long (30x12x12"). I realize that's going to leave the ends of the tank rather dim while the middle is super bright. I'm ok with this and planning my rock scape to support it.

Since the tank is only 12" deep I'm thinking optics are not required. If I go with no optics how high above the water should I hang the lights? Should I use optics?

 

How many watts???

 

88watts total.

40w of 5w white (1:1 cool/warm)
27w of 3w royal blue/blue (6:3)
9w of green/cyan
3w red
9w uv - but I'll probably dim these way down

Every color is on its own dimmable channel so I can adjust the color temp to my liking.

 

If you don't use optics they will light up the entire room. You might do 90 degree so it will light up the ends better because you should still get good par with only 12 inches of water.

 

+1

 

Does this math look right?

If I put the lights 6" from the water with 80 degree optics with the 10" heatsink centered (8" led to led) over a 30" tank, I'm looking at 9" from either end dark on the surface and the light to extend 1" past the tank on the bottom.

Math:
Tan 40 x 6" + 4" = 9", 18-9= 9"

Tan 40 x 18" + 4" = 19", 18-19= -1"

Sounds good to me if I did everything right.