Heat light set up

Was just hoping to get the opinion of resting the heat light on the top of the cage. I have just recently moved and don't have the whole set up for my heat lamp yet - however it is very cold where I am and if I don't run the risk of hurting my birds by having the light resting on the cage I would prefer to keep my little finches warm. They don't make contact with the roof from all the times I've watched them.

All replies are appreciated, thank you!