The number of Christmas lights that can safely be connected to a single outlet depends on several factors, including the wattage of the lights, the type of outlet, and the electrical capacity of your home. As a general rule of thumb, it's best to limit the number of lights per outlet to around 100-200 watts, or 10-20 standard 10-watt Christmas lights. This will help prevent the risk of overloading the circuit and causing an electrical fire or other hazards. If you have more lights than this, consider using multiple outlets or power strips to spread the load.