wonder why they produce two different voltages in the first place? It seems that more drivers can support he 36v version more so than the 72v version. I can run four 36v 35990's on a 350mA driver, a 700mA driver, a 1400mA driver, and even a 1750mA. I can also run two 36v 3590's on a 2100mA driver. Most of these are not available to the 72v version COB. For the 72v COB you can run the 240H versions for pairs at higher amperage and four at lower amperage. Fewer availabilities to run the 72v at lower amps to gain the inefficiencies available to the 36v COB. yes the 36v COB is more efficient at 23W while the 72V can only run at 49W with a lower efficiency. You just figured it out. I run my 36v COB's at 175mA, 350mA, 700mA, 1400mA, etc. flexible and efficient. lower heat, higher efficiency. peace