a average human on a cycle puts out 1/10th of a hp and can only do that for about 1 hour (session lenght on a excercicle varies but 20 min is normal) a stepper would put out slightly less. What this means is your out put per human is 32.5 watt hours per user per machine (750 watt=1 hp) or you would require 3 people grinding away to power one single 100 watt bulb…just dont make sense.