Small cabinet ventilation/light measurement issue

I'm starting a small grow in a divided wardrobe cabinet under CFLs (one 250w). I don't want to cut any holes for vents if I don't have to, as I will probably be moving up to a grow tent in the future and may be using the wardrobe as intended in the future.

I'm thinking of leaving the door cracked a small amount with a box fan directed into the space. I think I'll have enough lumens still to do well and this is fine for daylight hours, but how long do you think I can shut the door during darkness before ventilation becomes an issue? I can get a small fan for inside the cabinet but I'm assuming that's not going to work without a fresh air intake.

If I do need to cut a hole in the flimsy backing for a fan, how would I keep light out during darkness while still getting ventilation? There's no room for ducting and I'd rather not have any ducting show anyhow.

i started my grow in a closet but i was having heat and light leak issues. that was with a holes cut in the door with an intake and powerful outtake fan.i moved them to a smaller cabinet but with the same intake and outtake fans and now im good.to keep light out i use dryer vent on the intake and out and give it a few 90 degree angles.

I'm not thinking light leaks will be much issue. The room the cabinet is in is an interior room, pretty dark even during daytime. I plan to further work on limiting light from outside the room using heavier curtains and a new shade, and fixing the door to the room.

By the time I have to go to 12/12 the place will be like a cave.