depending on size of the housing, number of CREE LEDS (CREE are the best out there IMO, for the price), and Kelvin rating. seems the 6500k are more $ then the 10k (or equivalent) but not much. the power consumption is MUCH lower then a Power Compact or Metal Halide, less heat and lower electric bills!! i love my EVO72s...never have to replace bulbs, less power, more light...WIN WIN WIN!!!
what size 40 do you have?? ive seen people call 29s a 30g and the dimensions of a 30 are waaaaaaaaaaay different then a 29....so depth matters too....
it was the best bang for the buck vs buying a Marineland for 350-up....for my 72"