half-value angle, <for a diffusing surface, by reflection or by transmission>
angle of observation at which the luminance has half the value of the luminance of the diffused light at the angle of 0°, with perpendicular incidence of the light
Note 1 to entry: For indicating the shape of the scattering indicatrix it is recommended that the diffusion factor, σ, be used for strongly diffusing materials, and the half-value angle, γ, for poorly diffusing materials.
Note 2 to entry: The half-value angle is expressed in radian (rad) or degree (°).
Note 3 to entry: This entry was numbered 845-04-90 in IEC 60050-845:1987.
Note 4 to entry: This entry was numbered 17-515 in CIE S 017:2011.