Well I'm glad I haven't ordered any parts yet because I'm not pleased with the efficiency and PAR output, mainly because of the Vero 18s. I'm now thinking of 16 Vero 29's instead of 24 Vero 18s to cover a 4 foot square. I'll still build 4 " fixtures" but each will cover a 2' x 2' square. Spacing the COBs 1' each way, 2 per 23" heat sink. The Vero 29 is 44.5%+ efficient at 1.4 amps so each heat sink deals with 56W. 23" of the 5.88 profile comes out 107cm2/w, a bargain at $40.02. Unfortunately the driver match is not as pretty with the Vero 29, until the HGL-240H-C1400B is available I'll use the HGL-120-C1400B to drive 2 cobs. Roughly $300 in material yields a 200W fixture that'll deliver 22.25 par watts /sq ft. Now I'm thinking of adding some red "stars" to shift the spectrum for flowering and use up some of the excess driver capacity. The drivers will allow addition of 20 red stars, maybe more, to each heat sink (2 parallel strings of 10, about 29.4W) but that's probably pushing the heat sink. What efficiency are red stars?