Luminosity (L) is the measure of energy, or power emitted by a star.
It is measured the same way we measure the energy output of a lightbulb.
Lightbulbs come in different strengths: 40 watts, 60 watts, or 100 watts, for instance.
A watt is a unit of energy emission.
The Sun’s luminosity, or energy output, is about the same as 4,000 billion trillion 100-watt light-bulbs.
One degree of luminosity (1 L) is equal to the Sun’s luminosity.
The star Sirius has a luminosity of 30 (30 L). It puts out thirty times more energy than the Sun.