Calculation of the effective emissivity of a cavity having non-Lambertian isothermal surfaces

A method to calculate the directional local effective emissivity for a cavity having non-Lambertian isothermal surfaces is presented. Numerical calculation is carried out for a cylindrocone. The directional local effective emissivity directed to the cavity bottom is smaller than that directed to the cavity opening, and the local effective emissivity for a Lambertian takes a value close to the middle. The integrated effective emissivities are computed for a nonimaging system and an imaging optical system.