how to detect burned out christmas lights

A burned-out Christmas light bulb will no longer emit any light or produce a glow. If you shine a flashlight into the bulb, it may appear dark or black inside. In addition, the bulb may feel hot to the touch, or you may notice an acrid smell coming from the bulb. A simple test is to hold the bulb against your cheek and feel if it's warm. If it is, the bulb is likely burned out and needs to be replaced.