They do not have the intelligence to correspond 'hand' - 'food'. The only thing that means there is food, is the scent and appearance of prey.
Your hand does not look and should not smell like their prey. If they are going to bite you, it is either upset or scared, not trying to bite you for food.
I do not suggest feeding outside the enclosure. It heightens the risk of being bitten as well as having problems with regurgitation and stress from the situation.
Snakes would much rather be left alone in the dark to eat then be watched with bright lights shining.