One bulb will emit heat. This bulb may be a regular household bulb or a special reptile bulb. It will say it emits UVA but basically it is just for heat. If you are using clamp lamps you will need another clamp lamp or a total of two. In this clamp lamp will be a special, more expensive UVB bulb. It will say it emits UVA but basically it doesn not emit much heat at all, hence the reason you need two fixtures and two compact bulbs.
The only case you will not have two bulbs is when you are using a Mercury Vapor Bulb (MVB) which is only recommended to use on tanks above 55 gallons. This special bulb emits both the proper amount of UVB but also a lot of heat and should be placed in a ceramic fixture that allows a lot of wattage and be placed about one foot away from the basking area.




