LED Pool Lights are now available. Although initial cost is more, but they can save you money by using less electricity and lasting a lot longer than the old Incandescent lights
Incandescent pool lights are come in different Watts, and they are 110 volts. Since they are immersed in water, they have to be connected to a GFCI breaker for safty.
12 Volts lights are now available, which makes them safer for under water usage.