Hey
If the light is a UV stipe light and its ot used to heat the vivarium, there is no need to put a safty cage around it since it will not get hot enough to burn the snake.
But if its a heat bulb which you are heating the vivarium with, I would put a metal safty cage around it because the snake is bound to try and get up on to it sometime and when it does it will come of with some bad burns and may even et an infection and die.
Good luck
Alex