There are two types of circuits; a series circuit and a parallel circuit. The components of a series circuit are connected end to end; the amount of electric current flows through its components. The more bulbs connected the dimmer they become because less electric flow. If one bulb blows, the other bulb will not light up. This is because it is considered as an incomplete circuit.
The elements of a parallel circuit are connected in such a way that each component has the same voltage across its terminal; the electric flows is divided among its parts. In a parallel circuit, the bulbs and switches are arranged in parallel. The bulbs are connected side by side. The current is divided equally. If one bulb blows, the other bulbs stay lit because they each have their own circuit and electricity keeps on flowing through the circuit.