Definition – An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated to a high temperature, by passing an electric current through it, until it glows with visible light (incandescence).

Working Principal –

A bulb consists of a glass housing which is filled with inert gas, two lead in-wires which are connected with a filament. When we switch on electricity, the current passes through the lead in wires & reaches filament which is made of Tungsten. Tungsten has very high melting point i.e. 2482° C). Now filament will heat up so much that it’ll glow red or white hot and give off light. The tungsten is very thin and is used in coil form which offers maximize resistance in the wire. When electricity passes through the filament, it gets heated up &glow.

The tungsten is placed in the glass housing for two reasons – 1) It protects people from hot filament and 2) it also keeps oxygen away from the hot metal, which would make it immediately burn up.

The bulb is usually filled with a low pressure, inert gas such as argon. The function of argon is to stop the oxygen in the light bulbs from corroding the hot tungsten filament.The use of argon in light bulbs prevents the evaporation of the tungsten filaments, which results in increased light bulb life.

Disadvantage of incandescent bulbs- As almost all electricity fed to bulb is converted into heat, therefore, energy consumption is high in such bulbs (almost 80% energy wasted in heat generation).


Range of bulbs–5W, 25W, 40W, 60W, 100W & 200W.These bulbs are available in different – different colors such as clear, milky, red, yellow etc. Such bulbs are fixed in a holder. These holders are available in various designs.

(Note– These days such bulbs are being used in very limited area due to high power consumption. Such bulbs have been replaced by CFLs & LEDs)

BULB HOLDERS – Holders are also available in different shapes & sizes. Mostly, two types of holders are available in market – pin type & thread type. Pin type holders are standard holders whilethread type holders are available in different threads e.g. E10(Mini Screw), E11(Mini Candelabra), E12(Candelabra),E14(European),E17(Intermediate),E26(Mediam),E27(Mediam),E39(Mogul), E40(Mogul),EX39(Extended Mogul).