The Dreaded Dead Bulb: How to Spot and Solve the Problem on Your Artificial Christmas Tree
So, what's your reason for asking?
Has all the lights on your artificial Christmas tree gone out?
Quite likely, the bulb has broken off the socket. Check the string of lights and replace the bulb with any of the replacement bulbs you got during purchase.
If you replace burnt bulbs immediately they go out, the string will last longer, and that’s because the current running through string remains the same.
Keeping the number of bulbs in the string less will make the remaining bulbs burn hotter and shorter-lived.
Before storing the strings of lights, you should check for any faulty bulb and replace without delay.
Do you check them unlit to see which is toast?
Seeing if a bulb has burned out or lost its filament will indicate which bulb is defective on your string of traditional Christmas lights.
In many cases, the bulb will also be "smoked". There will be some blackening inside the bulb. The rest of the lights will usually stay on if only one bulb is burned out, unless a tiny wire resembling a hair at the base of the bulb is also faulty. (That wire keeps the string of lights on if a bulb burns out because it continues to conduct electricity.)
Reinstall the darkened bulb and connect the set once more to a single outlet. It is possible the wiring harness is malfunctioning if the light string does not come on again. In that case, stop working with the lights string and go for a new one.
You’d save yourself the stress of replacing the entire string of lights or getting a completely new tree if you act early. So stall no further. Get down to your artificial Christmas tree and sort the bulbs.