luminosity

Luminosity is a measure of the total amount of energy a body radiates per unit time. In astronomy, it represents the intrinsic radiative power of an object, independent of its distance from the observer. It is distinct from apparent brightness (or flux), which depends on distance and intervening material.

The bolometric luminosity sums emission over all wavelengths. It is commonly expressed in watts or as a ratio to the Sun's luminosity, L/L☉. The solar luminosity is about 3.828×10^26 watts.

For a star approximated as a blackbody, luminosity relates to radius and effective temperature by L = 4πR^2 σT_eff^4, where σ is the Stefan-Boltzmann constant. The observed flux F at distance d is F = L /(4πd^2); therefore L = 4πd^2F. Astronomers also use bolometric corrections to infer L from measurements in a limited wavelength range.

Common variants include spectral luminosity, which specifies luminosity per unit wavelength, and monochromatic luminosity at a given frequency or wavelength.

In everyday language, luminosity can denote brightness of a light source; in physics, it is a fundamental intrinsic property of an object that characterizes its total energy output.