Lights for a 75cm tank

[Epiphyte]

Got Shades? Chihiros - Shade - RGB VIVID II - black

Nope I do need to get them, but sadly Aquasabi aren't shipping to UK right now and Green Aqua shipping costs are a little high. I'll lower the lights to see if it helps but it's not the end of the world. I've got some 1.5mm aluminium sheet lying around so I could make something myself until I find an easier source of shades.

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..
View attachment 163344

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..

Thanks @oreo57, this sort of stuff is fantastic information which is a little beyond what I would have worked out on my own. I'll drop the lights to 9cm and see how it goes. The corners of the tank mostly have stems in them so lighting isn't as crucial as the centre which has carpeting plants, so I can sacrifice a little corner light intensity.

Thankfully I've made some convoluted aluminium extrusion light fixing which is really adjustable for height, even beyond what the suspension wires can give.

 

[alto]

Don’t forget that as you reduce light intensity (running at say, 60% vs 100%), light distribution pattern also alters
(this pattern is easy to see with a Kessil over an empty tank in a dark room)

 

[oreo57]

Don’t forget that as you reduce light intensity (running at say, 60% vs 100%), light distribution pattern also alters
(this pattern is easy to see with a Kessil over an empty tank in a dark room)

Don't think the pattern changes, just gets more visible to the eye..
Gamma Basics

Like you can spot differences between 20% to 10% then 100% to 50%
Whole thing is complicated..

GUIDE TO TIR LENSES - LEDiL

WHAT IS A TIR LENS Most typical lenses in the LEDiL standard product range are the cone-like lenses. These lenses are often called TIR lenses as a big part of their design relies on total internal reflection. Typically TIR lenses are rotationally symmetrical designs which give a nice round light...

www.ledil.com

 

[alto]

just gets more visible to the eye..

perhaps ... but my plants also noticed - shade is shade