 Radiative flux

Radiative flux is the first angular moment $F_{\nu }=\int I_{\nu }\cos \theta d\Omega$ of specific intensity and measures net radiant power crossing unit area. Integrating over frequency gives bolometric radiative flux. The receiving surface's orientation matters through $\cos \theta$; observed radiative flux from a compact distant source conventionally refers to an area perpendicular to its line of sight.

Radiative flux, often referred to as radiant flux, is a measure of the amount of radiant energy (such as light or thermal radiation) that passes through a given surface area per unit time. It is typically expressed in watts (W), where one watt equals one joule of energy per second.