The structure of a light bulb is fairly simple. At the base, there are two small metal contacts which are connected to the ends of the electric circuit. These metal contacts are attached to two hard wires. These wires are attached to a fine metal filament. This filament stands in the centre of the bulb, held in place by a glass mount. The filament and all the wires are encased in a glass bulb which is filled with an inert gas, like argon.

When a light bulb is connected to a power supply, the electrical current runs from one metal contact to the other, moving through the filament and all the wires. Electrical current in a solid conductor is measurable by the movement of free electrons (ones that detach themselves from atoms) from an area with a negative charge to an area with a positive charge.

As the electrons zip along through the filament, they are constantly bumping into the atoms that make up the filament. The energy of each impact vibrates an atom — in other words, the current heats the atoms up. A thinner conductor heats up more easily than a thicker conductor because it is more resistant to the movement of electrons.