The factor sinϑdϑdφ is an element of solid angle, dω, and the factor cosϑ is needed to convert the projected area of radiance back into physical area. \...The factor sinϑdϑdφ is an element of solid angle, dω, and the factor cosϑ is needed to convert the projected area of radiance back into physical area. πF=∫2π0∫2π0L(ϑ,φ)sinϑcosϑdϑdφ=∫2π0∫1−1L((μ,φ)μdμdφ