Electrons moving across the filament in the light bulb cause the light bulb to light.
The 3 components of any functioning circuit are:
- voltage source - provides a reason for electrons to travel in your circuit.
- current - moving electrons
- resistor - slows the flow of electrons in the circuit
Note, if the circuit does not provide a closed path, electrons will not flow. There needs to be a connection from the negative side of the battery through the light bulb and out to the positive side of the battery in order for the light bulb to light.