If you're using a white light for heat during the day, you would have to replace it with something else at night that would provide the same heat without the light. A much easier option would simply be to use the same "nightlight" all the time.


And a 40 watt bulb will not provide the kind of heat you need to achieve optimum temperatures and gradient. You should look for a UTH (Under Tank Heater) and a means to control the amount of heat it puts out (either a T-stat or rheostat/dimmerswitch). If your enclosure is in a particularly cool room, you may need some type of bulb or second UTH to warm the "cool" side of your gradient.

However you go about it, it should be set up to stay the same day and night.