Optical quantities

ratio of the speed of light in vacuum to that in the medium

measure of how strongly an optical system converges or diverges light

measure of directional energy flux

right|thumb|320px|Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light-gathering area of the previous one.

material dispersion property

angle of incidence for which all reflected light will be polarized

physical quantity

power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy

natural logarithm of the ratio of incident to transmitted radiant power through a material; the absorbance × ln(10)

physical quantity

term

proportion of observed intensity to ideal intensity, in astronomical imaging

optical path length through Earth’s atmosphere for light from a celestial source

how much a beam expands as it travels

concept in optical lens design

distance over which a propagating wave maintains a certain degree of coherence

concept in laser optics

the time over which a propagating wave (especially a laser or maser beam) may be considered coherent

thumb|Conservation of etendue

wavelength interval over which the magnitude of all spectral components is equal to or greater than a specified fraction of the magnitude of the component having the maximum value