Why is my light not working but has power?

When your light is not working but you have confirmed it has power, there are several possible causes depending on whether you mean a garage door opener light, a house light, or a light fixture. For a garage door opener light, if the opener itself works and moves the door but the light does not come on, the most common cause is a burned-out bulb, especially if it is a standard incandescent that failed from vibration. Try a new bulb. If a new bulb does not work, the light socket may have a loose wire, corroded contacts, or a failed relay on the logic board that controls the light circuit. The logic board can fail so that the opener motor still works but the light circuit has no power. Also check if the light button on the wall control is set to off or if the motion sensor is disabled. For a regular house light fixture that has power at the breaker but the bulb does not light, causes include a bad bulb, a failed switch, loose wire nuts in the junction box, a tripped GFCI outlet upstream that cuts power to that circuit, or a bad neutral connection. Use a non-contact voltage tester to confirm power at the socket itself, not just at the panel. If the socket shows power but the bulb does not light, the socket itself may be faulty and need replacement.