Spot lights work great for a basking light. You may be better off buying a lamp from a hardware store and then buying a special uv/heat bulb from a pet store. To my knowledge they work good.
use a 5.0 uvb bub and a deep dome. also *depending on tank size, turtle size, and room heat* it will be good to get a heat bulb. they are endothermic so keep the tank temperature around 78-82deg to maintain a well regulated digestion and overall body function.