Magnetic field 'magnetic field' is used to describe as well as or in place of . There are many alternative names for both (see sidebar). In SI units, is measured in teslas (symbol: T) and correspondingly (magnetic flux) is measured in webers (symbol: Wb) so that a flux density of 1 Wb/m is 1 tesla. The SI unit of tesla is equivalent to (newton·second)/(coulomb·metre). In Gaussian-cgs units, is measured in gauss (symbol: G). (The conversion is 1 T = 10000 G.) One nanotesla is equivalent to 1 gamma (symbol: γ). The -field is measured in amperes per metre (A/m) in SI units,
Spectral flux density of the two-stream model of the radiative field, which is reasonable for a field that is uniformly stratified in flat layers, when the base of the hemisphere is chosen to be parallel to the layers, and one or other sense (up or down) is specified. In an inhomogeneous non-isotropic radiative field, the spectral flux density defined as a scalar-valued function of direction and sense contains much more directional information than does the spectral flux density defined as a vector, but the full radiometric information is customarily stated as the spectral radiance (or specific intensity). For the present purposes, the light