Luminosity is emitted radiative power: the energy carried away by electromagnetic radiation per unit time, measured in watts. Bolometric luminosity includes all wavelengths; a measurement through one photometric passband captures only part of it. Spectral luminosity records how that power is distributed over frequency. Received observed radiative flux has different units, watts per square metre, because it measures what crosses an observer's collecting area. [ref].
For example, an ideal source with luminosity emits each second regardless of whether it is viewed from or parsecs. Its observed radiative flux changes with distance, while its luminosity remains fixed. Combining stellar parallax with observed radiative flux therefore lets us compare the actual outputs of stars rather than their apparent brightnesses.
Luminosity generally refers to the intrinsic brightness of an object, particularly in the context of astronomy. It is the total amount of energy emitted by a star, galaxy, or other astronomical object per unit time, typically measured in watts or in solar luminosities (where one solar luminosity is the luminosity of the Sun).
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