out sections on the tree when I was taking it down. Those are sections of 48 lights where every single bulb is burned out, often with a dark discoloration inside the bulb. I’ll have to get more bulbs to fix it, either that or just retire the tree and get a new one. I’ve kept this tree working for many years now.

In case you didn’t know, leaving burned out bulbs in an incandescent light string reduces the life span of the rest of the bulbs. An incandescent mini light string consists of 48 2.5V bulbs wired to evenly divide the 120V across all bulbs (2.5V x 48 = 120V). Sometimes they round that up to 50 bulbs (so each bulb is a little under voltage and dimmer than it should be) and often they combine these sections with other 48 bulb sections to get longer strings. When a bulb burns out, it breaks the circuit so all bulbs go out. To prevent this, each bulb has a shunt device inside that is designed to melt and short circuit if the bulb does burn out. That completes the circuit so the other lights remain lit. But it also means that now the other bulbs are running on higher voltage (120V is now divided by 47 instead of 48, so each bulb is now getting 2.55V instead of 2.5V). This shortens the life of those remaining bulbs. When the next bulb burns out because of its reduced lifespan, the voltage to the remaining bulbs goes up even more which reduces even more the time to the next burn out. Eventually you get to a scenario where the voltage per bulb is so high that they all blow.