Since Christmas tree lights run on a circuit, power gets cut to the rest of the strand. If you could only find that one bulb, you can replace it with a new one.

You may have seen the LED Keeper and LightKeeper Pro gadgets in hardware stores by the Christmas trees. LED Keeper is for strings of LED lights, Lightkeeper Pro is for incandescent light strings.

Since Christmas tree lights run on a circuit, power gets cut to the rest of the strand. If you could only find that one bulb, you can replace it with a new one.