i think it would be 4128lm/55watts, not 4800, though. "mean" is the arithmatic average, i think the chart is saying that the initial output for a brand new bulb is 4800lms, but that the average output, once the new-ness wears off is more like 4128lm. which makes sence with the next column, because 4128/55 = 75% efficiency. in that case, (4128*130)/55 = 9757.0909 repeating. personally, i would say "around 10k lumens" and consider it good enough. ;P

the weird thing, to me, is that neither of the lights i was looking at fit that chart. one says it has 12000lm/125watts (=98% efficency) which seems high and the other one has 7900lm/150watts (=52.7% efficency) which seems high. also, i have no idea what the "k" number in the light descriptions is, like "150W 6500K 7900 Lumens."

jeeze, this post took like half an hour...i would be in bed, but i saw my catt is losing another leaf because it doesn't have enough light, and it brought me back here..

EDIT: heh, neither of those posts were there when i started! :P

footcandle = 1 lumen per square foot. so the more lumens, the moore FCs, and also the close to the bulb the more FCs. as for light per orchid, according the the AOS pdf, catts (for example) like around 5k FCs, which should be providable with either a 7.9k lm or a 12k lm light, hung at different distances. from what i've read here, it seems like catts want as much light as they can get without getting scorched, though. all i know is mine is not getting enough.