Alightbulb has an efficiency of 13.1%. how much light energy (not heat energy) is generated by the bulb every second if the bulb has a power of 8 w?

where J is Joules.

Explanation:

The watt (w) definition is

Given that the bulb has a power of 8 W this means that every second the bulb emits 8 Joules of light energy. This would be true If the bulb has an efficiency of 100%. The efficiency indicates the amount of energy that its converted into light energy and the amount of energy that its converted into heat energy (wasted energy).

The lightbulb has an efficiency of 13.1%, meaning that every 100 J of energy that the bulb emits, 13.1 J will turn into light energy and 100 J  - 13.1 J  = 86.9 J  will be wasted into heat energy.

To obtain the light energy generated every second by the bulb, we need to obtain the 13.1% of the bulb's power :

We find that is the light power, this means that every second the bulb emits 1.048 J of light energy.