CXB 3590, would be a 70% efficient lamp compared to a 64% efficient lamp. There have been a few 700ma lamps built, no 350 that I know of.
thats because once you get below 700 mA your money is better spent on more lights
it costs twice as much in cobs to get from 64 to 70% efficiency. Wouldnt you really have double the garden size at 64%?
the 'break even' point of array cost vs efficiency is different for everyone, i personally think 60% is the saweetspot
when i make a spreadsheet and look at overall system cost for a 5x9 tent i see:
18 cobs - 44.1% eff., $1800, $2.26/ PAR W
24 cobs - 49.6% eff., $2216, $2.48/ PAR W
48 cobs - 60.25% eff., $3900, $3.59/ PAR W
70 cobs - 63.7% eff., $4673, $4.07/ PAR W
96 cobs - 67.1% eff., $6388, $6.61/ PAR W
or in other words, 3 tents at 50% eff vs 2 tents @ 60% eff vs 1 tent at 67% eff