Running at 200 mAmps
Running at 400 mAmps
At 200 mAmps I measured 30 micromols PAR at 3" above the substrate, and at 400 mAmps, 45 micromols at the same location. At 200 mA I got about 45 micromols just below the water line, and at 400 mA I got about 100 micromols at that location, and about 80 micromols at about 4" below the water line. All of those measurements were in the middle of the tank.
The PAR remained constant just below the water line at about +/- 8 inches from the center going from end to end, and dropped in half right near the end. From front to back the PAR remained constant at about +/- 2" and gradually dropped to half at near the front and back. The plants kept me from making that type measurement further down in the tank.
At 400 mA I have about the PAR I was hoping for, possibly a bit low, but not much, and I can always lower the fixture a little to increase it. Right now the LEDs are 7 inches above the tank rim.
The shimmer is fascinating. Every leaf, every ripple and every fish casts multiple shadows on the substrate and the lower leaves. It is disconcerting at first, but in 30 minutes it didn't bother me. And, the light has been on about 30 miinutes now, with the heat sink not even feeling warm.
EDIT: The actual calculated current these are running at is 425 mA for each parallel string, or 850 mA total, for a total power consumption of 40 watts. The light intensity I'm getting is almost exactly what I was getting with a 55 watt GE9325K bulb in an AHS bright kit, mounted at the same location. So, this is using 73% of the power for the same amount of PAR.
Because the light is distributed over most of the footprint of the tank, and not coming from just a small area, the rise in intensity as you go up in the tank is not nearly an inverse square relationship, but is much closer to being linear. So, the intensity near the waterline isn't as high as I would expect from a typical aquarium light giving the same PAR at the substrate. (This is a good feature.)
It has been about an hour now, and the heatsink is still not even warm, and, of course, the lights are still working - a miracle!