Energy-saving lamp

This is the Sankey diagram for a typical LED lamp:

100 joules of electrical energy is converted to 75 joules of light energy and 25 joules of heat energy

Efficiency = \frac{\text{useful output energy}}{\text{total input energy}}

Useful output energy = 75 J

Total input energy = 100 J

efficiency = \frac{\text{75}}{\text{100}}

efficiency = 0.75

This means that 0.75 (or 75 per cent) of the electrical energy supplied is transferred as light energy.

For every £100 spent on lighting, £75 is spent on the light and only £25 is wasted heating the surroundings.

The LED lamp is much more efficient than the filament lamp and can help save money.