a 400 watt is going to be massive in that space,, I was going to suggest a 250 watt, but if the 400 is already on the way, there is going to be a minimum spacing required for a 400 watt bulb and space or height is going to become an issue, the CFL bulbs you have now allow for some real close spacing, but wont yeild as much,,,
you can make light traps out of cardboard and tape over the outside of those fans to block light, just make an S shape with the cardboard and tape it over the fans, on the outside if you have room,, my light traps are on the inside of my box, but i have more height than yours,
is smell or odor control a concern?,,, if so those pc fans are going to have a hard time moving enough air and pushing air thru a carbon filter,, so a fan upgrade may be in your furture,,
you also may have to use a cooling tube for that 400 watt bulb, but that will require a better fan,, but it will help with temps
you can also tape cardboard to the inside of one of the doors where they over lap and that would help light seal the door somewhat,,, i use weather stripping on my doors to seal the air and light,,
hope this helps some