That might indeed be a problem. In most of the places where chams come from (Madagascar, Africa, Yemen) they only experience a maximum of about 13 hours of light a day. That's why most keepers try to stick to a 12 hour light cycle. Bright sunlight streaming through the window at 'night' would most likely disturb their sleeping habits.
Can't you draw the curtains in the room where you keep them?
Putting a cover over them would limit ventilation in the cage, and possibly prevent it from drying out properly overnight, but it might well be the only practical thing to do. Just make sure your lights aren't on auto-timers that might turn on with the covers still on and start a fire.
I'm sure some of the Canadian keepers on this forum might be able to help you out. Unfortunately (or rather fortunately) I've never had to deal with this problem where I live.