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Dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency. [1] Sometimes the term chromatic dispersion is used to refer to optics specifically, as opposed to wave propagation in general. A medium having this common property may be termed a dispersive medium.
The Germans, however, dissented and decided to use a definition equal to 9/10 of the output of a Hefner lamp. In 1921, the Commission Internationale de l'Eclairage (International Commission for Illumination, commonly referred to as the CIE) redefined the international candle again in terms of a carbon filament incandescent lamp .
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).
This is a result of the prism material's index of refraction varying with wavelength (dispersion). Generally, longer wavelengths (red) undergo a smaller deviation than shorter wavelengths (blue). The dispersion of white light into colors by a prism led Sir Isaac Newton to conclude that white light consisted of a mixture of different colors.
In optics, optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device: P = 1/f. [1] High optical power corresponds to short focal length.
In optics and lens design, the Abbe number, also known as the Vd-number or constringence of a transparent material, is an approximate measure of the material's dispersion (change of refractive index versus wavelength), with high values of Vd indicating low dispersion.
Another example is incandescent light bulbs, which emit only around 10% of their energy as visible light and the remainder as infrared. A common thermal light source in history is the glowing solid particles in flames , but these also emit most of their radiation in the infrared and only a fraction in the visible spectrum.
In the United States and Canada, lamps are typically identified by a code such as FxxTyy, where F is for fluorescent, and the first number (xx) indicates either the power in watts for bi-pin lamps, length in inches for single-pin and high-output lamps, and for circular bulbs, the diameter of the circular bulb.