How do you know which bulb is out on your Christmas lights?
So, why are you asking?
Did all the lights on your light string go out?
More than likely, a bulb has come out of the socket. Visually inspect the light string and replace the bulb with one of the replacement bulbs that came with the set.
If you don’t have a replacement handy, you can use from a string that is exactly the same as a source of replacements. Keep this in mind when you are ordering quite a few light strings. Order one extra string to be a source of bulbs for all the others when their bulbs burn out.
Replacing burned out bulbs as soon as they go out extends the life of the entire string since the same current runs through the string. With fewer bulbs in the string, the remaining bulbs will burn hotter and their lives will be shortened.
At the end of each Season, it’s a great idea to check for any dead bulbs and replace them before storing the light strings away.
Are you looking at them unlit to find the one that is toast?
You can tell which bulb is out on your string of traditional Christmas lights by looking for the bulb that is “burned out” by looking at the tiny little filaments in the light bulbs to see which bulb is “burned out” or has lost it’s filament.
Many times the bulb will be “smoked” as well. The inside of the bulb will be a little blackened. Normally, if a bulb is just burned out, the rest of the lights will stay lit unless a tiny little wire that looks like a little hair at the base of the bulb has also lost connection. (That little shunt wire is what continues to conduct electricity and keep the light string on if the bulb burns out.)
Replace the blackened bulb and plug the set back into an outlet alone. If the light string doesn’t come back on, a problem with the wiring harness may be indicated. If that’s the case, stop using the string of lights and replace it with a new string.