Unfortunately i dont have a light meter...this is the 5th run i have done at 24 hours on(each run 80 days) as well as another 2 season of 2 month + vegging of outdoor plants. To date i have seen no reduction in yield, actually yields have been quite good(shooting for 1 gpw on the run i just finished). Still not comparing them to the effectiveness of cobs, but for the guy on a major budget they arent a bad bunch of lights at all!! (mars 100X3, galaxy hydro 100X3). I chose the 3w models because i have a very cramped space and thought they would be the best choice with limited vertical.