yeah I agree on that ChilLED stuff @Enzyme303, definitely a short list of players at that level. I dunno how cost effective they are Scone...
But really yeah they are swimming in that 2.5mmols/watt and above level, and very few are up there, hard to argue with really. Also worth looking at is Pacific Light Concepts for a plug and play COB system that they will see you right on price with probably if you want a fair bit, think these are running about 2.0mmol/watt, just ask them; the owner is a guy with much experience in this sort of stuff and one of the early COB builders on several sites years ago, much of his youtube stuff was what got me taking COB seriously to begin with. Fluence Bioengineering is also one i would normally suggest but recently I hear they took a turn for the worse on some manufacturing decisions and the product is now a little subpar, but I have never used one so take that as the hearsay it is
As far as building them yourself, cheapest is the various Citizen chips (ask Forest, he will be more familiar than I with these), highest performance at low power is Cree CXB3590 (make sure you buy the top bins only), best bang for buck in my humble opinion is Vero 29, which is cheaper than Cree but also a tad more effective than most Citizen chips. Check out the datasheets, it won't take you long to see what I am talking about and make your own decisions. Another company called Luminus is maybe worth a look too. Much might be decided by availability where you are in the end, you probably want a US supplier like RapidLED for COB DIY in the States, otherwise Digikey or other large electronics wholesalers hold stock of them, and if you are lucky or willing to wait and shop around the big online shops you might find some chips at a good price
But really any of those four manufacturers are pretty good and your budget and how hard you intend to drive the chips also comes into play, with Vero outdoing Cree in lumens per watt performance at higher wattages at the chip, (once you get above 75w) right up to 100w... but honestly most of the magic in COB is found in the gentle running power, otherwise at 100w a chip, lumens per watt falls into the HPS range, so you kinda outsmart or should I say outcheap yourself at some point and the whole thing becomes worthless. I can testify personally that these Vero 29D based systems do very well up to the +-63w each range, I have never took them above that so I can't talk about that from experience. But if money is no object, i go Cree all day. I would pay extra for the binning alone if i could afford it, and these work beautifully at +-50w and do things you thought only happened in dreams when you go down to +-30w and below, talking like 200 lumens per watt and above at the chip level, with a spectrum you can shape yourself to a fair degree by chip choice and selective dimming :kill:However, building them at this low power gets expensive very quickly with the amount of chips and heatsinks required
if it were me DIYing a whole show of that size today and with a US address, I would probably move away from COB towards quantum boards, they are hard to beat in pretty much every way, including the heatsinking, which is a big part of doing COB properly and QBs don't even need sinks if run at a certain level. You could talk to Horticulture Lighting Group who are the main supplier of these and in partnership with Samsung directly, who supply them the diodes. They can tell you exactly just how much wattage on what board would require a sink or not. Could be quite a saving in a big show to not need all that heatsink, definitely worth checking out. Of course HLG also sell finished 550w fixtures that look very nice and would probably damn near equal a 1000w single ended HPS in performance, especially in a cross-lit room with a lot of fixtures. Think GrandMasterLevel had a youtube side by side going for a while, was pretty telling, might still be up if you have a look
expect to use around 60 - 70% of the wattage of HPS for equal performance... This is just a guideline really and chip selection, kelvin temp, drive power etc all factor into it, maybe a little less wattage with a QB than a COB, they are more efficient after all
Hope you manage to get the ball rolling anyway Scone, sounds like a whole bunch of fun