Incandescent light bulb

A typical incandescent light bulb. The filament is the thin wire stretched between the vertical contact wires and held up by two other support wires.

Incandescent light bulbs are devices that convert electricity into light by heating a filament, using electric current, until it emits electromagnetic radiation. As current passes through the filament, its high resistance causes its temperature to rise until it glows. This effect is known as incandescence, and it is the guiding principle behind the traditional light bulb (see figure 1). The light bulb filament is about 3000 K, so it gives off blackbody radiation, which (as shown below) means a lot of energy is going into heat.

Incandescent light bulbs is still a remarkably widespread method of lighting but other types of light bulbs (like LED and CFL) are growing more popular. This shift is due to the extreme inefficiency of incandescent bulbs as they only convert about 10% of the electrical energy they receive into visible light, with the rest being dissipated as heat.[1] In Canada, legislation has been place since 2014 to phase out incandescent bulbs with alternatives like halogen lights, CFL light bulbs, and LED light bulbs.[2]

Phet Simulation

The University of Colorado has graciously allowed us to use the following Phet simulation. Explore this simulation to see changing temperature changes the amount of radiation given by a light bulb filament. All of the radiant energy to the right of the rainbow in the simulation is energy coming off as heat (infrared radiation):

For Further Reading

For further information please see the related pages below:


  1. Edison Tech Center. Incandescent Lamps [Online}. Available:
  2. Natural Resources Canada. Canada’s standard for efficient light bulbs [Online]. Available: