This is a good question, and I have some experience with this scenario.
If your cage height is not great and you use temperature control that limits the output from the bulb (i.e. proportional controller or a dimmer) then chances are the bulb won't be on high enough where 1" away will burn flesh or do damage within the reaction time of the snake to move away.
If you crank a high-wattage bulb on full, then 1" away can be a little close.
In any case, it is the surface of the bulb that does damage, where you or the snake can get burned before your brain tells you to pull away from the bulb. As long as you shield the bulb surface you are pretty much preventing injury. Personally, for ceramic bulbs I try to have a minimum of 1 1/2" clearance. If you already have wire cages that only have 1" of clearance, you can simply make a square from 3/4" pine molding around the ceramic socket, and attach the wire cage to the molding, thus giving you an extra 3/4" of space away from the surface of the bulb on top of the space you already have.