I balked when I saw the price tag on those heatsinks. I refuse to pay more for heatsinks than COBs! So I decided to try a DIY approach: 3" by 2" by 0.25" copper under the COBs and then a 6" long aluminum rectangular heatsink constructed from 2" wide by 0.125" fins with 0.5" x 0.25" spacers between them. It would be too small but I will have them covered with exhaust air flowing over them. Did a LOT of research on heatsink sizes and I came up with this. But I plan to build one and then experiment to see what it does to the temperature with a resistor load. If I have to add more fins, that will be very easy.
I got some heat transfer silicon grease to put between the COB and the copper and the copper to aluminum junction as well. We’ll see how it does.
I planned to put them in pairs on a long box so I can hook up flexible duct to get air flowing through them. Each pair would separate the cobs by about 2 feet. I think this will fit my new grow area well. It’s 5 feet by 3.75 feet. (Yes, it’s a bathtub we never use. Nice to have built-in drainage.)