Many people think that you have to drain the pool in order to perform a pool light repair. In fact, your pool light is like a sealed cup. This allows us to work on the light housing above water.It is easy to get the light out of the pool and disassembled but it very tricky to get everything back together PROPERLY and sealed watertight. Because of this, I recommend that you have a licensed pool repair contractor make the necessary repair.
In Orange County, FL you do not have to have a contractor's license to clean a pool but you do need one to work on the pool equipment. Many people do not know that their pool cleaning company is not qualified to work on their pool equipment. You do not want someone training themselves on your equipment. You can check the Florida Business & Professional Regulation's website.
Whenever we do an Orlando pool light repair we always change the lens gasket. This is essential in order to keep water from entering into the housing and ruining your light socket. The typical cost with our company for a light repair is $94.99 service call + ~$12 lens gasket + ~$20 bulb.
One quick thing to check is your ground fault interrupt (GFI.) For the pool lights that run on 120v current (as most residential's do) you must have a GFI installed in series with your light. This is usually near the pool timer box and looks just like an outlet in your bathroom. It has the familiar "push to test" and "reset" buttons. With the summer thunderstorms in the Orlando area it is very common to have these things trip. It can also be a breaker in your breaker box near your pool timer. Look for a reset button on one of the breakers that may have tripped. Hopefully, I saved you a service call.
If you pushed the reset button and tried the light again only to have the reset button re-trip, you more than likely have water in your light housing. This is usually due to the lens seal going bad. Water in the housing is extremely bad and you should have it fixed as fast as possible to keep the socket from permanent damage.
Another cause for the GFI tripping is a bad light cord. The only repair for this is pulling a brand new light at the cost of ~$300.