Fuses are essentially fire breaks, points of deliberate weakness that, if power surges through a house’s electrical system, will collapse to prevent damage or fire. This is achieved by the fuse’s central component, a strip or strand of metal which has a lower breaking capacity. The metal’s breaking capacity is the maximum current that can be passed through it safely, while anything above that will cause it to melt and break the circuit. Zinc, copper, silver and aluminium are all commonly used as fuse wire.

The fuse wire is then placed between two terminals, wrapped in a non-conductive material and then put in place. Then, if a power surge happens, the fuse will break, severing the connection, closing the circuit and minimising further damage.

The coloured lights need some sort of power source, which usually comes in the form of a lithium battery at the bottom of the candle (separated from the wax so the battery won’t burn). Connected to this battery inside the candle are LEDs, most commonly three, which give off the three primary colours of light – red, blue and green. Different combinations of brightness in these LEDs causes the light to mix which yields many different colours.

So how do the coloured LEDs switch on when the flame is lit? An optical sensor runs from the top to the bottom of the wick in the candle and is connected to the LEDs and battery at the bottom. As soon as the wick is lit, the optical sensor detects light from the flame, which activates the circuit.

Author: Rik Sargent, Science Museum