If you just had bulbs replaced then you may have water in one of your fixtures. You will need to find the junction box for the lights. It's going to be a two x two x three inch box sitting on a condute a foot to eighteen inches from the ground, with four screws holding the top on. Their can be one or two of these depending how many lights you have. From each light you will have a black wire with three wires in it. you need to remove the wire nuts and undo these wires then try to turn the power on. If the GFI still kicks then you can look for shorts, but if not then you will need to hook each light up seperatly to see when the GFI kicks. This light will be the problem. Even a small amount of water will cause problems so you wont nessarly see the water. If this is a small pool light you will probally need to replace the light fixture. Most of these are quartz lights and can be replaced with incandesent. These will last much better. If it is a large light you can probally open the light on the deck and turn for a half hour or so to dry it out and be sure to use a new gasket when you put it back together as it may seem tight when you put it back together but expansion and contraction when the light is on will cause leaks by it self. Let me know how you do. If you just had bulbs replaced then you may have water in one of your fixtures. You will need to find the junction box for the lights. It's going to be a two x two x three inch box sitting on a condute a foot to eighteen inches from the ground, with four screws holding the top on. Their can be one or two of these depending how many lights you have. From each light you will have a black wire with three wires in it. you need to remove the wire nuts and undo these wires then try to turn the power on. If the GFI still kicks then you can look for shorts, but if not then you will need to hook each light up seperatly to see when the GFI kicks. This light will be the problem. Even a small amount of water will cause problems so you wont nessarly see the water. If this is a small pool light you will probally need to replace the light fixture. Most of these are quartz lights and can be replaced with incandesent. These will last much better. If it is a large light you can probally open the light on the deck and turn for a half hour or so to dry it out and be sure to use a new gasket when you put it back together as it may seem tight when you put it back together but expansion and contraction when the light is on will cause leaks by it self. Let me know how you do.