illuminance (at a point of a surface) [*E*_{v}; *E*]

1. quotient of the luminous flux d*Φ*_{v} incident on an element of the surface containing the point, by the area d*A* of that element

2. equivalent definition: integral, taken over the hemisphere visible from the given point, of the expression *L*_{v}cos*θ*d*Ω*, where *L*_{v} is the luminance at the given point in the various directions of the incident elementary beams of solid angle d*Ω*, and *θ** *is the angle between any of these beams and the normal to the surface at the given point

Unit: lx = lm·m^{-2}

Theme by Danetsoft and Danang Probo Sayekti inspired by Maksimer