Irradiance

(At a point of a surface) quotient of the radiant flux incident on an infinitesimal element of surface containing the point, and the area of that element. Note 1 to entry: Convective heating is negligible in the horizontal specimen orientation. For this reason, the term “irradiance” is used instead of “heat flux” throughout this part of ISO 5660 as it best indicates the essentially radiative mode of heat transfer.