No, it's more lumens. You CAN add them up if you like, you can't just say "oh I have 2 bulbs that output 1000 intitial lumens each, so that means I have 2000 lumens". Nobody really knows what you have in that example, but it's less than 2000 lumens.
8x 42watt cfls is 336watts
@900lms each, = 7200lms
thats just maths nothing to do with growing, i have no idea why that guy thinks you will lose any lumens.
but they are spead over a larger area
although you should be getting a lot more lumens than that. i have some 20watt cfls and they give out 1200 lumens each. you sure they use 42watts? to get 900lumes they should only be using around 15watts