I assume your talking temperature in Celsius so that's be about 5-14 Fahrenheit in the garage. I think you'd be safer in the cellar. With that said I have successfully overwintered pots by putting the up against the wall attached to the house, covering with a blanket then piling bags of leaves around it to insulate. Garage gets to about 0 Fahrenheit on the coldest night here in Zone 4. Don't worry about light.

Yes I'm in Canada where we are metric, so our temps are in Celsius. But I didn't want to confuse the matter so I just mentioned below and above freezing numbers. I would love to try the cold cellar but I don't know how easy it would be to carry that huge pot full of soil that far and down stairs. Good to know they don't really need light when dormant.