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An emission coefficient (often indicated as j) is a measure of a substance's electromagnetic radiation (EMR) emission in a particular direction, increasing the total EMR leaving in that direction over that passing through. For example, giving a glowing gas, at any point within it, a certain amount of EMR is emitted in all directions and the emission coefficient quantifies the amount emitted in some specific direction. The coefficient is the energy of the EMR emitted in that direction along a unit length in that direction, from a given cross-section, and a given density of the material. (The amount EMR from an exact mathematical point would be none, so the emission coefficient is quantified as the value of a distribution function.) The coefficient depends upon the substance and its density. It is somewhat like the inverse of an absorption coefficient, but it is less dependent on the amount of EMR passing through. (Stimulated emission implies some dependence on passing EMR, but one convenient variant on terminology is to include stimulated emission in the absorption coefficient, considering such emission to be negative absorption, and to define the emission coefficient as independent of passing EMR, i.e., just quantifying spontaneous emission.) These coefficients are used for modeling the effect of gas on EMR passing through (radiative transfer), e.g., in modeling stellar structure, gas clouds, and atmospheres.