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The Stefan–Boltzmann equation applied to a black body gives the value for luminosity for a black body, an idealized object which is perfectly opaque and non-reflecting: [11] =, where A is the surface area, T is the temperature (in kelvins) and σ is the Stefan–Boltzmann constant, with a value of 5.670 374 419... × 10 −8 W⋅m −2 ⋅K −4.
Photometry is a branch of optics that deals with measuring light in terms of its perceived brightness to the human eye. [1] It is concerned with quantifying the amount of light that is emitted, transmitted, or received by an object or a system.
The object's actual luminosity is determined using the inverse-square law and the proportions of the object's apparent distance and luminosity distance. Another way to express the luminosity distance is through the flux-luminosity relationship, = where F is flux (W·m −2), and L is luminosity (W). From this the luminosity distance (in meters ...
In astrophysics, L is used for luminosity (energy per unit time, equivalent to power) and F is used for energy flux (energy per unit time per unit area, equivalent to intensity in terms of area, not solid angle). They are not new quantities, simply different names.
Brightness, the subjective perception elicited by the luminance of a source; Luminance, the photometric equivalent of radiance (lm·sr −1 ·m −2) Photometry (optics), measurement of light, in terms of its perceived brightness to the human eye; Radiometry, measurement of light, in absolute power units; Luminosity
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.
The relationship is represented by the equation: = where L ⊙ and M ⊙ are the luminosity and mass of the Sun and 1 < a < 6. [2] The value a = 3.5 is commonly used for main-sequence stars. [ 3 ] This equation and the usual value of a = 3.5 only applies to main-sequence stars with masses 2 M ⊙ < M < 55 M ⊙ and does not apply to red giants ...
Illuminance diagram with units and terminology. In photometry, illuminance is the total luminous flux incident on a surface, per unit area. [1] It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness perception. [2]