When the circuit closes, which means all cables are connected properly, the potential difference (voltage) applied to the circuit from the battery forces the free electrons to move from the point with the low potential to the one with high potential in other words from the negative pole of the battery to the positive one. This flow of electrons is called electric current.
The light bulb (incandescent lamp) is like the ones used at home. The enclosure of the lamp is a bulb made of thin glass. Inside the glass are inert gases such as nitrogen and argon. In the centre there is a very thin wire (called filament) made of tungsten. Tungsten is a metal that melts at an extremely high temperature. When electricity passes through the wire, it becomes warm. As the temperature increases, the wire almost melts and it then starts illuminating like all hot metals do. This illumination is the light.
The energy is, thus, transformed from electrical 
to thermal (heat), and then from heat to electromagnetic radiation (heat and light).
The incandescent bulb was invented in England by Joseph Swan in 1878 and then, independently, (a year later) by Thomas Edison in the USA.
How much power is used by a light bulb?
You need:
light bulbs
bulb holders
some cables with crocodile clips at the end
1 battery 4.5 Volt
A 9 Volt battery can be used. In this case appropriate light bulbs should be used too, else they will be destroyed
AA or LR6, or any other cylindrical battery can be used; in this case a battery holder is necessary.
