Although a 100 watt bulb will produce heat, it is not enough to prevent pipes from freezing. Pipes are most likely to freeze when the temperature outside dips below 20 degrees Fahrenheit. To prevent your pipes from freezing, you should:
-Wrap them in insulation or heating tape
-Seal any cracks or openings in your home that could let cold air in and make sure your doors and windows are properly sealed
-Let faucets drip overnight so that water is moving through the pipes and not sitting still which can cause them to freeze