I have a few things to add about Chip On Board (COB) LEDs. COB was never meant for grow light applications. It was originally designed to meet the needs of high-output pinpoint source lighting for street and area lighting, car headlights, etc. As such, they don't really work well in grow applications, where the idea is to cover a greater area, yet in close proximity to, our plant bed. Additionally, because of the greater heat you mentioned in your post, it is necessary to reduce current to the COB package to maintain lifespan of the device. As you rightly mention on your web site, LED output is not linear, in terms of current:lumens, and this reduction of current to reduce heat takes its toll on true light output. I pulled some of the efficacy (lumens per Watt) figures from a COB LED (30W) manufacturer. While the claim at full power is about to 92lm/W for "cool" white devices, this is in a lab and it is highly unlikely this can be achieved in the field. Even at half power, the relative luminous flux is derated to about 45% of the initial lumens. Thermal derating at 90degC (max junction temp for these COBs is 120degC) will shave 20% from the output. You wind up with about 30-35% of the original relative luminous flux OTF (Out The Front) of the luminaire (light fixture). This gives you about 1080 lumens out at 15W, or 72lm/W. I've built and tested a lot of luminaires over the past decade and this is a generous number.