Generally speaking if you have 1 enclosure and your ambient temps is below healthy range the best option is to have a heat pad and a thermostat on each side.

This way you can provide a cooler end around 78/80 and a warmer end around 88/90.

This solution is the most efficient way with only one snake, now if you had multiple animals and a dedicated herp room a oil filled heater would be the best option.

Heat lamp work but it will dry out your enclosure and since glass tank do not hold humidity this might not be the best solution for you.