you can buy this rolled up , black plastic sheet at Wal Mart that is used for gardens.. just hang up on one side like a curtain...
i taped some mylar to one side of the black plastic , and then hung the black plastic and mylar from the ceiling inside the growroom, right in front of door..
100% light stays in the room..
with just the black plastic hanging, no light goes through...
cheap, easy fix for that light leak...

PEACE!
slim