The solar luminosity, L_☉, is a unit of radiative (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars.

One needs to distinguish between the Sun's actual measured radiative luminosity (), which is variable at the ±0.1% level, and the Sun's long-term average luminosity which has been adopted by astronomers as a standard unit of power for quoting the luminosities of celestial objects (e.g. stars, galaxies, etc.). The latter was recently defined by the International Astronomical Union as the nominal solar luminosity () which corresponds to a power of exactly 7026382800000000000♠3.828×10 W or 7026382799999999999♠3.828×10 erg/s.