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Luminosity functions are used to study the properties of large groups or classes of objects, such as the stars in clusters or the galaxies in the Local Group. Note that the term "function" is slightly misleading, and the luminosity function might better be described as a luminosity distribution. Given a luminosity as input, the luminosity ...
The CIE distributes standard tables with luminosity function values at 5 nm intervals from 380 nm to 780 nm. [cie 1] The standard luminous efficiency function is normalized to a peak value of unity at 555 nm (see luminous coefficient). The value of the constant in front of the integral is usually rounded off to 683 lm/W. The small excess ...
Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. [1] [2] In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a star, galaxy, or other astronomical objects. [3] [4]
The dashed red line is an example luminosity function when the Malmquist bias is not corrected for. The more numerous low luminosity objects are underrepresented because of the apparent magnitude limit of the survey. The solid blue line is the properly corrected luminosity function using the volume-weighted correction method.
In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit.
Factor ()Multiple Value Item 0 0 lux 0 lux Absolute darkness 10 −4: 100 microlux 100 microlux: Starlight overcast moonless night sky [1]: 140 microlux: Venus at brightest [1]: 200 microlux
The mesoscopic luminosity function at wavelength can be written as the weighted sum, [12] = ′ + (),where () is the standard photopic luminosity function (peaking at 683 lm/W at 555 nm) and ′ is the scotopic luminosity function (peaking at approx. 1700 lm/W at 507 nm), and standardized by CIE and ISO. [13]
According to this function, 700 nm red light is only about 0.4% as efficient as 555 nm green light. Thus, one watt of 700 nm red light is "worth" only 2.7 lumens. Because of the summation over the visual portion of the EM spectrum that is part of this weighting, the unit of "lumen" is color-blind: there is no way to tell what color a lumen will ...