I installed the new Chihros light today and it's good.... I think! I've yet to get the colour rendition how I like it, it just feels "wrong", if that makes sense. The colours on my fish really pop though, they're quite stunning, especially the blue edge on the fins on one of my Apistogramas.
I would post a picture but the tank is going through it's ugly stage with fungus from the new wood everywhere
@oreo57 you mention the light to be hung 12cm off the water line, how did you get to this figure? I've got it perhaps 20cm off right now but it's a little blinding from my sofa with the light bleed.
Actually my math was way off. Not sure how I got 12 (may have somehow doubled my should have been est of 6cm) but here is a corrected graphic of various heights and light err "cone"
I'll blame it on the metric system...
I assume 12" width (75x30).. height is irreverent.
Keep in mind that the edge area around an ind. "cone" will be considerably duller than the center area.
You can see the issue w/ 20cm..
You can use this calculator to get an idea of the spread of the light.
It will give you a diameter but you only use the radius
Example you light surface is 60x14cm
At a throw distance of 6cm the diameter of a single 120 degree lensed diode is 20.78cm
So your spread is
10.39 + 60 + 10.39 = 80.79
10.39 + 14 + 10.39 = 34.78
(yes just add diameter plus light )
LED Lighting Beam Angle Calculator
Once the light is in the tank it is "trained" by reflection/refraction.
Hopefully I got this right .. but the concept is sound.
Oh and to give you a number ..at 20cm your "cone of light" is 129 x 83.3cm..
Edit: Looking over my older post and I can see that I was concentrating on evening out the PAR which does change things a bit..
That's my story at least..
Split the difference.. 9cm..