You need to tell us what your setup is, i.e. size enclosure, where the basking spot is etc.
I like to use a 40w lamp set on a timer to come on for about 6hrs a day in summer, BUT, it is connected to a thermostat set to 30c. When temps in my room get hot it obviously doesn't come on. I also use just a low wattage compact flouro attached to a timer to give a day/night cycle.
Also my thermostat probe is placed next to the basking spot just out of the direct heat of the lamp because that's the only part of the enclosure I want heated.
As said previously highly variable depending on your setup. Put up some pics and more info and we`ll be able to help you some more with more detail.
You`ll love the diamond, great snakes and in my opinion not any harder to look after, they just have different needs.
