Electric lamps

Ordinary electric lamps contain a thin metal filament that glows when electricity passes through it.

However, most of the electrical energy is transferred as heat energy instead of light energy.

Filament lamp
Filament lamp

Modern energy-saving lamps and LEDs (light-emitting diodes) work in a different way.

They transfer a greater proportion of electrical energy as light energy.

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

From the diagram, you can see that much less electrical energy is transferred, or 'wasted', as heat energy from the energy-saving lamp.

Led light bulb
LED lights

It's more efficient than the filament lamp.

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