One of the first jobs when putting up a Christmas tree is untangling and testing the lights.

Traditionally, it always seemed to be the case that they wouldn’t work, so your would spend the next hour changing one bulb after another to find and replace the faulty one, which, inevitably, would be at the opposite end of the string to the one your started at!

This is because, in the past, Christmas tree lights were wired in series.  One light would be wired to the next, ten the next, and so on, until the required length was reached.


The problem with wiring in series is that if there is a fault anywhere along the circuit which prevent the current flowing, the circuit is broken and none of the lights will work. This could be down to a blown bulb or damage to the wires themselves.  Whatever the cause, until the problem is located and sorted, the lights will not work.

More often than not thought, tree lights are now wired in parallel.  Sometimes t’s the whole string, but with longer lengths, it tends to be banks of a fixed number that are wired in series and then each bank is in parallel with the others.


The advantage of wiring in parallel is that the current flowing round the circuit has different paths to flow down, meaning that if there is a problem on one path there are other options, meaning that most of the lights will stay on.  At the worst, a bank of lights ay be out, but the rest should remain bright,

But why do we have Christmas tree lights in the first place?

Originally, it was candles on that were put on the tree, held in place with wax or pins and was done to light up the ornaments on the tree, but once electric lights were invented, they became the standard.

In recent years, LED lights have taken the place of incandescent bulbs because they are more energy efficient.

Until next time, keep calm and apply some Science!

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