Nothing to worry about. The plants will naturally start loosing the leaves that arnt worth having so they can use their energy on flowering.

As for lumens, it's something like 2000 per sqaure foot or so, i think. I cant even remember. I just have two 250 watt HPS's.

WHat lights are you using and what wattage? Also how many plants and/or space is it covering, and also how close is the light. The plants dont look like their stretching so it must be enough.

Also have a look about the place, theres a whole load of growing forums where you'd get more responces.

By the way, welcome to the boards.