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 拢100 spent on lighting, 拢75 is spent on the light and only 拢25 is wasted heating the surroundings.
The LED lamp is much more efficient than the filament lamp and can help save money.