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For example, if JE(λ) is spectral radiance with the unit W/m 2 /sr/m, then the quantal equivalent JQ(λ) characterizes that radiation with the unit photons/s/m 2 /sr/m. If CE λi ( λ ) ( i =1,2,3) are the three energy-based color matching functions for a particular color space (LMS color space for the purposes of this article), then the ...
Spectral radiance Specific intensity L e,Ω,ν [nb 6] watt per steradian per square metre per hertz W⋅sr −1 ⋅m −2 ⋅Hz −1: M⋅T −2: Radiance of a surface per unit frequency or wavelength. The latter is commonly measured in W⋅sr −1 ⋅m −2 ⋅nm −1. This is a directional quantity. This is sometimes also confusingly called ...
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).
For propagation of light in a vacuum, the definition of specific (radiative) intensity implicitly allows for the inverse square law of radiative propagation. [12] [14] The concept of specific (radiative) intensity of a source at the point P 1 presumes that the destination detector at the point P 2 has optical devices (telescopic lenses and so forth) that can resolve the details of the source ...
A luminance meter is a device used in photometry that can measure the luminance in a particular direction and with a particular solid angle. The simplest devices measure the luminance in a single direction while imaging luminance meters measure luminance in a way similar to the way a digital camera records color images.
Relative luminance follows the photometric definition of luminance including spectral weighting for human vision, but while luminance is a measure of light in units such as /, relative luminance values are normalized as 0.0 to 1.0 (or 1 to 100), with 1.0 (or 100) being a theoretical perfect reflector of 100% reference white. [1]
Radiance is the integral of the spectral radiance over all frequencies or wavelengths. For radiation emitted by the surface of an ideal black body at a given temperature, spectral radiance is governed by Planck's law, while the integral of its radiance, over the hemisphere into which its surface radiates, is given by the Stefan–Boltzmann law.
The Eddington approximation can be used to obtain the spectral radiance in a "plane-parallel" medium (one in which properties only vary in the perpendicular direction) with isotropic frequency-independent scattering. Extracting the first few moments of the spectral radiance with respect to yields
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