Wow, I missed that chart above before. So you pump in 1750umol over 4x4 (=about 1200umol average per m2) and then you are left with an average of only 826umol/s/m2? Which means that only 70% of the light actually reaches the plants. The rest is wasted on the walls because it hangs so high (40cm).
That's why I prefer strips over boards. Hang 8 separate 112cm strips and you can hang the light at 20cm (actually less even). Saves you half the wall losses. Actually 4 strips would already be sufficient to cut the hanging height in half compared to the boards.
Which means that 600W of strips will give you the same amount of photons on the plants as you get from 700W of boards!
Let's not be dishonest here – you can throw as many LED boards as you can fit in a 4'x4' and realise much better efficiency. That's the first point.
The second point is, when LED manufacturers calculate efficiency, they do it at a set current: commonly 65mA for 3V mid-power (3030) LEDs. So here is an efficiency test on our boards at roughly that level. This test also directly correlates to two more PAR maps I have calculated below.
2.47 umol/j at 1.5A.
The PAR map in the previous post (
August 2019) was for four boards at 3.5A per board (as you can see in the Dialux program top left). At that much higher current, the boards have been tested at 2.17 umol/j – so your calculation is not correct (there appears to be another issue with your calucation, but I'm sure you'll work it out).
I can see how you would have assumed they were running at 2.5 umol/j and not 2.17, because of the ambiguity surrounding "advertised" efficiencies vs efficiencies at higher currents. So I will take the blame for that. I simply posted a real-world example of four boards in a 4x4 running at 676W at 2.17 umol/j. I didn't know it was going to be dissected by you. After all, you've had me on ignore for a long time – haven't you?
Here are eight boards over the same area at 1.5A per board (560W total) at 40cm at 80% wall reflectivity – these boards are running at a true 2.47 umol/j:
Here is the same configuration at 20cm:
So at 40cm, 560W of LED boards is producing an average of 1023 PPFD and at 20cm it is 1150 PPFD. What's more, if you were running CO2, your plants would be right in the Goldilocks zone under even the hottest spots produced by the boards at 20cm (1350 PPFD). But if you weren't, you would run them at 40cm – because the average PPFD might be slightly lower (down 11%), but the coverage is more even.
It's still more efficient than your strips, and I guarantee the boards provide more even coverage. At least, based on what you have written, because you haven't posted a PAR map of your own set-up yet.
Of course, you can also play around with the board configuration (move them closer together) to get higher average PPFD readings, but you lose the even coverage and introduce more hot-spots. With strips, you are always going to have hotspots directly under each strip at such low hanging heights, and the only way to prevent that is to move the strips closer together – much like a board(!).
If we ever get to see your PAR maps, that's probably what we will see.