I believe a Mercury Vapor Bulb (MVB) would be the most efficient starting point for a new tort.
There are many options available, from florescent tube, Compact Florescent (CFL, which have been causing eye issues, best avoided), and Red and Blue incandescent.
Tort's require UVA and UVB light, so a light that produces UV will be your best option for a healthy tort. MVB and Florescent can both produce UVA/UVB, however, not all do. You should look for specialty bulbs for reptile care. Incandescent bulbs do Not produce UV wavelengths of light.
Florescent lighting is cheaper on energy consumption, however a separate heat source would be needed to provide a basking spot of 90~99*F. Whereas an MVB will provide plenty of radiant heat for a basking spot as well as the UV requirements.
I hope that helps to point you in the right direction. And I'm sure we'll have some other members chime in with further insight for ya.
Good luck with getting your new tort and im sure you'll have an amazing time when you get one!
Your lighting/uvb/heat requirements will be dictated by your enclosure, and what works for one may not work for you. Opinions vary greatly so, IMO, it is best to read as much information as you can.