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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 ...
Spectral radiance Specific intensity L e,Ω,ν [nb 3] 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 ...
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.
An example of spectroscopy: a prism analyses white light by dispersing it into its component colors. Spectroscopy is the field of study that measures and interprets electromagnetic spectra. [1] [2] In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum.
A rainbow is a decomposition of white light into all of the spectral colors. Laser beams are monochromatic light, thereby exhibiting spectral colors. A spectral color is a color that is evoked by monochromatic light, i.e. either a spectral line with a single wavelength or frequency of light in the visible spectrum, or a relatively narrow spectral band (e.g. lasers).
A tristimulus colorimeter measures the tristimulus values of a color. [4] A spectroradiometer measures the absolute spectral radiance (intensity) or irradiance of a light source. [5] A spectrophotometer measures the spectral reflectance, transmittance, or relative irradiance of a color sample. [5] [6]
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 ...