Energy-saving lamp
This is the Sankey diagram for a typical LED lamp:
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.