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In astronomy, a period-luminosity relation is a relationship linking the luminosity of pulsating variable stars with their pulsation period. The best-known relation is the direct proportionality law holding for Classical Cepheid variables , sometimes called the Leavitt Law .
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
A coefficient of utilization (CU) is a measure of the efficiency of a luminaire in transferring luminous energy to the working plane in a particular area. The CU is the ratio of luminous flux from a luminaire incident upon a work plane to that emitted by the lamps within the luminaire. As a ratio, the coefficient of utilization is unitless.
The lumen is defined as amount of light given into one steradian by a point source of one candela strength; while the candela, a base SI unit, is defined as the luminous intensity of a source of monochromatic radiation, of frequency 540 terahertz, and a radiant intensity of 1/683 watts per steradian.
Mathematically, for the spectral power distribution of a radiant exitance or irradiance one may write: =where M(λ) is the spectral irradiance (or exitance) of the light (SI units: W/m 2 = kg·m −1 ·s −3); Φ is the radiant flux of the source (SI unit: watt, W); A is the area over which the radiant flux is integrated (SI unit: square meter, m 2); and λ is the wavelength (SI unit: meter, m).
It is around six or seven times as massive and five thousand times as luminous as the Sun and is located around 2,000 light-years away from Earth. [2] Its radius is 58.5 times that of the Sun. [7] The radius, temperature, luminosity, and colour are all variable as the star pulsates during its eight-day period. The period is slowly increasing. [2]
In astrophysics, the mass–luminosity relation is an equation giving the relationship between a star's mass and its luminosity, first noted by Jakob Karl Ernst Halm. [1] ...
Luminous efficacy (of radiation) K: lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to radiant flux: Luminous efficacy (of a source) η [nb 3] lumen per watt: lm/W: M −1 ⋅L −2 ⋅T 3 ⋅J: Ratio of luminous flux to power consumption Luminous efficiency, luminous coefficient V: 1: Luminous efficacy normalized by ...