Nearly every source of light depends, at the fundamental level, on the release of energy from atoms that have been excited in some manner. Standard incandescent lamps, derived directly from the early models of the 1800s, now commonly utilize a tungsten filament in an inert gas atmosphere, and produce light through the resistive effect that occurs when the filament temperature increases as electrical current is passed through.

Sub-atomic activity within a conducting incandescent lamp filament results in resistance to current flow, and ultimately leads to the emission of infrared and visible light photons.

While a resistor opposing current, it is possible for emission of large amount of heat. In many circuits, heat is considered as a energy loss of resistors. But in bulb lamp, heat is useful to produce light. We are familiar about incandescent lamp. It has tungsten filament surrounded by an inert gas. When you turn the switch on, lamp glows in your home.

In the filament, electrons collide with other electrons and produce resistance to mobile electrons which is the cause for current. Collision of electrons produce vibration of atoms in the filament and vibrational energy, in turn, produces heat on filament. Only ten percent of this heat energy is converted to light energy.Tungsten filament can be heated for high temperatures (over 2000 º C) and the capability of tungsten without melting and evaporating is useful in bulb lamps.