Luminosity is the name of a series of physical quantities .
In photometry, luminosity is a luminous quantity , which is the luminous flux of radiation emitted from a small portion of the luminous surface of a unit area . It is equal to the ratio of the luminous flux emanating from the considered small surface area to the area of this area  :
where dΦ v is the luminous flux emitted by a surface area of d S. Luminosity in the International System of Units (SI) is measured in lm / m². 1 lm / m² is the luminosity of a surface of 1 m 2 emitting a luminous flux of 1 lm.
Analogue of luminosity in the system of energy photometric quantities is energy luminosity (radiance). Its definition is similar to the definition of luminosity, but instead of the light flux Φ v , the radiation flux Φ e is used . The unit of energy luminosity in SI is W / m².
Luminosity of the heavenly body
Luminosity in astronomy is the total energy emitted by an astronomical object ( planet , star , galaxy , etc.) per unit of time . It is measured in absolute units ( SI - W ; CGS - erg / s) or in units of the luminosity of the Sun ( L ☉ = 3.86⋅10 33 erg / s = 3.86⋅10 26 W)  .
The luminosity of an astronomical object does not depend on the distance to the object, only the apparent magnitude depends on it. Luminosity is one of the most important stellar characteristics, which makes it possible to compare different types of stars in the spectra — luminosity , mass — luminosity diagrams. The luminosity of the main sequence stars can be approximately calculated by the formula  :
where R is the radius of the star, T is the temperature of its photosphere , σ is the Stefan-Boltzmann constant .
The luminosity of the brightest stars is millions of times greater than the luminosity of the sun. The luminosity of quasars can exceed the solar one hundred trillion times  .
In experimental elementary particle physics, the luminosity refers to an accelerator parameter characterizing the intensity of collisions of particles of a beam with particles of a fixed target (the intensity of collisions of particles of two opposite beams in the case of colliders ). The luminosity L is measured in cm −2 · s −1 . By multiplying the reaction cross section for luminosity, the average frequency of this process at this collider is obtained .
The luminosity of the Large Hadron Collider during the first weeks of the run was no more than 10 29 particles / cm² · s, but it continues to increase constantly. The goal is to achieve a nominal luminosity of 1.7⋅10 34 particles / cm² · s, which corresponds in order of magnitude to the luminosities of BaBar ( SLAC , USA) and Belle ( KEK , Japan ). The KEKB collider holds the world luminosity record for accelerators with colliding beams - 2.11,110 34 cm −2 · s −1  .
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