Your snake needs heat, and if the light is the source of heat, then you probably want one for day and one for night. Your snake does not need UVB (fluorescent) light like a lizard or turtle does. There are lots of great sources of heat for reptiles... heat rocks are not one of them. Lights work OK, but can get expensive over time as they don't seem to last long. Tell us a little more about your enclosure, and we might be able to recommend a good source of heat.