As the filament are very thin and coiled their resistance increases. Therefore, in order to increase the resistance of the filament they are made thin and coiled.
The filament of an electric bulb is a thin coiled wire made of tungsten. The reason behind why the filament is coiled is to produce resistance. Resistance can be simply defined as Friction produces in the way of electric current. And due to the presence of resistance (Friction), the bulb can produce its light.To make the bulb produce more light, the filament is usually made of coils of fine wire, also known as the coiled coil.
filament wire of a bulb is very thin and given a helical shape to get more resistance and wire length, thus converting more electricity into thermal energy and as a result get more light out of it.The advantage of the coiled coil is that evaporation of the tungsten filament is at the rate of a tungsten cylinder having a diameter equal to that of the coiled coil. The coiled-coil filament evaporates more slowly than a straight filament of the same surface area and light-emitting power.
Because it contains far more data than a straight chain of atoms. The same applies to light bulbs, the coiled wire produces far more light at a higher temperature than a single, straight filament can.