Question

What does the energy efficiency ratings on products mean?

Answer 1

`"Efficency(%)" = "useful energy"/"total energy" xx 100`

Explanation:

On a product there will be an efficiency number, this tells you how much of the energy produced is useful.

For example, a light bulb may be `20%` efficient. If the bulb has a power of `"100 W"`, only `"20 W"` are useful, light energy, while the other `"80 W"` are waste such as sound or heat.