Advice on Lumia 5.2 LED placement, please.

[GlassReef]

I'd appreciate some advice from the experts. I'm building a set of LED lights for my 8ft long X 3ft wide tank. I'm using 12 of the 70 watt Lumia 5.2 chips. I'm mounting two chips each on 6 24" long heat sinks the pattern will look like this:

Here's a pic of the first 2 completed pendants to give some visible input for the pattern, above:

I'm having trouble deciding the distance I should use between the 2 chips on each sink. The pic shows them at 16" apart. Inside width of the tank is 34 inches. The heat sinks will be spaced evenly along the length of the tank (96"). Where would you suggest placing the chips on the heat sinks?

 

[Mark Bianco]

I am assuming by looking at the drawing that the fixture sits centered over your tank front to back if so then for the best equal spread then find the center point of your fixture then space them each 6" from the middle. So basically you will have equal lighting across the tank. That being said if your rock work is primarily all in the back and you are not worried about lighting the back then move them forward slightly.

HTH
Mark

 

[oreo57]

Depends on the height off the water line you are planning on.. and what you desire..
Full coverage from 0" or lower in the tank.

"Cone" angle is 120 degrees I believe

Chips could be right next to each other at 1 foot off the water line..

How deep is the tank?

 

[GlassReef]

Thanks for the replies. I originally thought I would space the LEDs equally, front to back - IOW, one 11" from the back and one 11" from the front, leaving about 11" between the 2. As I saw what that looked like over the tank, I started thinking that, maybe, I'm wasting PAR by having them so far apart. Does that make sense?

The tank is 22" deep and the Lumia's do have a 120 deg. cone angle. They are supposed to cover 18"X18" well.

I'm new to LEDs and my fear is that, after spending a small fortune on the components, I'll not achieve the best possible results because of less than optimal placement.

 

[oreo57]

Still need your planned hiegt from the water line but...

Lets consider one chip for now..and consider it a point light source also..

120 degree beam angle / the majority of the light in 90 degrees..

At 2" above the water line your cone of strongest light is 4" in diameter..

NOW here is where height comes in..

Say you have your light 6" off the water line.
Your cone is 12" diameter...

6" per "side"..
IF you want light from the top the 2 chips would need to be 6" off the glass..BUT that would put them 22" apart..
10" "dead space so to speak.. not ideal..

Soo...Raise the light to 10"...

20" cones.. So each chip should be 10" from the glass side..
Leaving the 2 chips separated in the middle by 14"
Centers now overlap (10 +10)


Height and ideal spread are interrelated..
Figure 9" from glass, 9" from water line.... 16" apart..close enough.. Pucks aren't point sources..ect

 

[GlassReef]

oreo57 - you just made the lights come on (no pun intended)! Thanks all...