| Definition: | 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.
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