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The SI unit of spectral radiance in frequency is the watt per steradian per square metre per hertz (W·sr −1 ·m −2 ·Hz −1) and that of spectral radiance in wavelength is the watt per steradian per square metre per metre (W·sr −1 ·m −3)—commonly the watt per steradian per square metre per nanometre (W·sr −1 ·m −2 ·nm −1).
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).
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. [1] It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given solid angle .
The material consists of PTFE powder that has been compressed into solid forms and sintered for stability, with approximately 40 percent void volume [clarification needed] to enhance scattering of light. [6] Surface or subsurface contamination may lower the reflectance at the extreme upper and lower ends of the spectral range.
Kirchhoff's postulated spectral radiance I was a universal function, one and the same for all black bodies, only depending on wavelength and temperature. The precise mathematical expression for that universal function I was very much unknown to Kirchhoff, and it was just postulated to exist, until its precise mathematical expression was found ...
Radiant intensity is used to characterize the emission of radiation by an antenna: [2], = (), where E e is the irradiance of the antenna;; r is the distance from the antenna.; Unlike power density, radiant intensity does not depend on distance: because radiant intensity is defined as the power through a solid angle, the decreasing power density over distance due to the inverse-square law is ...
The light at the image plane, however, fills a larger solid angle so the radiance comes out to be the same assuming there is no loss at the lens. Spectral radiance expresses radiance as a function of frequency or wavelength. Radiance is the integral of the spectral radiance over all frequencies or wavelengths.
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 ...
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