Final answer:
The efficiency of a light bulb is calculated by dividing the useful energy output by the total energy input. The formula for calculating efficiency is Efficiency = (Useful energy output / Total energy input) x 100%.
Step-by-step explanation:
The efficiency of a light bulb can be calculated by dividing the useful energy output of the bulb by the total energy input. In the case of a light bulb, the useful energy output is the light emitted by the bulb, and the total energy input is the electrical energy consumed by the bulb.
To calculate the efficiency, you can use the formula: Efficiency = (Useful energy output / Total energy input) x 100%.
For example, if a light bulb emits 800 lumens of light and consumes 60 watts of electricity, the efficiency can be calculated as: Efficiency = (800 lumens / 60 watts) x 100% = 13.33%.