The sun's luminosity is not exactly 1. Its luminosity is approximately 3.828 × 10^26 watts, which is the total amount of energy emitted by the sun per second.

In astrophysics, a common convention is used where the bolometric luminosity of the Sun (L☉) is defined to be exactly 3.828 × 10^26 watts. This convention simplifies calculations and allows astronomers to express luminosities of other stars relative to the luminosity of the Sun. Using this convention, if we say a star has a luminosity of 2L☉, it means the star emits twice the amount of energy as the Sun.