Pool Lights Are SERIOUS Safety Issues!!
 "The best protection for families is 
inspection, detection, and correction of electrical hazards in and 
around swimming pools, hot tubs and spas".  Remember
 that water and electricity don't mix. If you notice anything that 
"looks" questionable or possibly hazardous, have it checked out 
immediately. 
ESPECIALLY questionable would be:
- Water visible in the light fixture
- Light won't turn on
- Light fixture loose
- The GFI keeps "popping" and turning the light off
- The Circuit Breaker keeps "popping" and turning the light off
Underwater (UW) Lighting
 UW
 lights have become a common, standard item in all pools. There are many
 manufacturers of light fixtures 
Your
 UW lighting should give you few problems. Most bulbs will burn for 
1,000 hours before re-lamping is necessary. The light fixture itself can
 last quite a while too, however, corrosive pool chemistry and shifting ground, can weaken the fixture and the screws which hold it together, and this may necessitate replacement. 
The
 light fixture is gasket sealed to prevent water from reaching the bulb 
behind the lens, however water surrounds the entire fixture, keeping it 
cool. Do not operate the light for more than one second without it being
 fully submerged. The light requires submersion to prevent overheating and burn out. 
 Light doesn't turn on?
Check all breakers, fuses, switches and Ground Fault Circuit Interrupter (GFCI)
 outlets. Frequently, a GFCI outlet is wired into the UW light circuit. 
If the GFCI 'red button' has popped out, the power will not continue on 
towards the light. Ensure all of these switches are in the ON position. 
If you find that a breaker or fuse or GFCI continues to trip, and the 
light will not come on, you should call for service IMMEDIATELY, at this point to 
determine where this irregularity is originating.
 Don't keep trying to get it to turn back on.....STOP......and call for help and keep everyone OUT of the pool until it can be checked out!
Water behind the lens?
This
 is a startling observation for many to see. Many times the lamp 
continues to burn even with water surrounding the bulb. If you notice a 
line of water in the lens, the fixture should be removed. 
Re-lamping the fixture: 
Bulbs
 used in this application are not cheap, but your bulbs can be replaced and resealed if there is no water in the conduit. 
Replacing the fixture:  
 If
 corrosive water has eaten away at the fixture, or the cord and 
connections have become damaged, or if the junction box is being moved, a
 new fixture is in order.