= Luminosity
{title2=$L$}
{wiki}
= Bolometric luminosity
{synonym}
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. https://arxiv.org/pdf/1510.06262[IAU 2015 Resolution B2: Radiative luminosity and irradiance]{ref}.
For example, an ideal source with <luminosity> $10^{26}\,\mathrm W$ emits $10^{26}\,\mathrm J$ each second regardless of whether it is viewed from $20$ or $40$ <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.
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