flux density (1) (luminous)

The luminous flux at a surface divided by the area of the surface. (See also "illuminance" and "luminous exitance".)

(2) (radiant): The radiant flux at a surface divided by the area of the surface. (See also "irradiance" and "radiant exitance".)

(3) flux density (of particle radiation): The time rate of flow of radiant-energy particles emitted from or incident on a surface, divided by the area of that surface.

NOTE 1 The equation "flux density = N/A∙t" applies, where N, A, and t represent the quantities number of particles, area, and time.

NOTE 2 The unit symbol (e.g., cm^‑2·s^‑1) does not identify particle type. The particle name may be placed before the term, e.g., "neutron flux density", or in the spelled-out unit name, e.g., "neutrons per square centimeter second".

NOTE 3 Flux density is maximized when the surface is perpendicular to the direction of the emitted or incident particle flow.

References

JESD77-B, 2/00

JESD89-2#, 11/04