by foil paper, do you mean like aluminum foil? if so, i woud bet my money that is exactly what it is... they problem with that foil is that it causes hot spots, and may burn your plants, which is exactly what it looks like to me..
get rid of the foil, and if they aren't already, just slap some white paint up on the walls with either a flat white or semi gloss.. i just got done reading how semi gloss is like 75-80% reflective, and flat is like 80-85% reflective... that should definitely help you out a ton...