half-value angle (for a diffusing surface by reflection or by transmission) [γ]

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 Unit: rad, °

NOTE For indicating the shape of the indicatrix of diffusion it is recommended that the diffusion factor σ be used for strongly diffusing materials, and the half-value angle γ for poorly diffusing materials.

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