How high above water line is your LED

[BigB72]

How high is your LED off the water line?
I currently have my prime about 12 inches off the water. I’m debating low to about 8 inches.
I’m the currently building a canopy and Im thinking it will look a little funny to be that tall

 

[Roy Arena]

Mine are about 9 inches off the water. You lose spread the closer they are to the surface. I think as long as you don't have excessive light spill....you're good.

 

[redfishbluefish]

Don't ask me the reference, but I remember seeing somewhere that the ideal height is 14 inches off the waterline for LED's. I have mine at 13 inches.

 

[oreo54]

Depends on the lens angle, what you want covered, and where you want best "PAR"..

AI Primes have 80 degree lenses standard I believe. Diode "puck" is about 2"
At 6" off the water line the coverage is a circle of about 12" in diameter..

8" is about 15 1/2" diameter "circle"

If your tank is about 24" wide the somewhat ideal (if you want light to cover all depths i.e no "dead zones" near the top.)
sweet spot is around 12" off the water line (22" diameter cone)..

Some want max PAR at the floor so the height would be lowered from that "ideal"..

This would give you an idea about single diodes and lenses..and the math

LED Lighting Beam Angle Calculator

A simple calculator that determines spot size by a light's beam angle

store.marinebeam.com

That gives you the diameter..
For things like the "black boxes" you just use the radius on each side..add the dimension between diodes

A black box board is about 14x6"
Lenses are usually 90 degrees..

At 12" off the water line it will throw a coverage pattern of approx..
12 + 6+ 12 by 12 + 14+ 12

so 30" x 38"

For a 24" wide tank an "ideal" height (full coverage top to bottom) would be 9"
And about 32" end to end (really prob need some overlap so less than 32")

None of these are "exact" measurements and it gets a bit complicated w/ beam angle definitions but the POINT is
to maximize the light getting into the tank..
As you can see from the above most sort of "know" this but each tank dimensions need to be considered.. and goal..

Once into the tank glass reflections and water refraction tends to keep it in..

OH, and you can just "draw" the pattern at the height you want on a piece of paper..

 

[vetteguy53081]

Mine - 14”.
A lot will depend on type of light used and PAR readings

 

[Coralreefer1]

It would also depend on how deep your tank is? What types of corals you have? Coral placement is also a determining factor of LED light placement above water line.