There have been several debates in recent years regarding snake lights. For years, snake owners used the same lighting set-ups for pet snakes as we did other reptiles but now we know that some lighting elements are unnecessary for most kinds of snakes.
If you have a pet snake that is naturally from a temperate climate (not too hot, not too cold) and your house stays warm year round, you probably don't need much in the way of lighting for your snake.
UVB Snake Lights
With the exception of some of the less common pet snakes, UVB lighting is unnecessary for snakes. Will UVB lights hurt your snake? No they won't, and it may also increase their activity or coloration, but snakes can be perfectly healthy without the aid of special UVB lighting. If you do choose to provide UVB to your snake make sure they cannot get within 12 inches of the bulb, do not keep it on for more than 12 hours a day, and make sure no glass or plastic is blocking it (use wire mesh or screens instead). A fixture with a reflector (or a piece of aluminum foil adhered between the light fixture and where the bulb sits) is also ideal to help reflect the maximum amount of UVB rays onto your snake.
Heat Lights for Snakes
Depending on your kind of snake's specific temperature requirements, you may or may not need heat lights to maintain appropriate temperatures.
Many snake owners use under tank heating pads to keep the tank warm but it can be difficult to maintain and monitor proper temperatures with heating pads alone.
Heat lights, in addition to providing more measurable ambient heat, also offer a more natural day/night cycle for your pet snake than heating pads.
You can have two separate heat lights, each on a 12 hour cycle. Leave the daylight heat light (the white light) on during the day and turn the "night-glo" or nocturnal red or purple light on at night. This will simulate a natural day/night cycle and is especially important for nocturnal snakes. Without a proper light cycle your snake may become stressed, lethargic, and stop eating.
Incandescent heat bulbs come in a variety of wattages to provide your enclosure with the proper temperatures. The smaller your tank, the lower the wattage that is needed. You wouldn't want to put a ball python in a 10 gallon tank with a 150 watt bulb. It would get much too warm in the enclosure. Get a thermometer that you can move around inside the tank and check the temperatures on both sides and the level that your snake will normally hang out. Aim for a warmer basking spot and a cooler side to provide a thermal gradient to allow your snake to choose where they want to be.
Also be sure to place the heat bulb in a heat lamp with a ceramic socket, not just a work light from the garage. Heat lights with ceramic sockets are sold in any pet shop and are safer to use with lights that emit heat. Work lights typically have plastic sockets and will melt from the heat of many heat lights used with reptile enclosures.