Light scattering from small particles in liquids and transparent solids may lead to a loss in optical clarity. If the scattering particles are in the micron size range, the scattering is confined to small angles with respect to the direction of the incident light. The resulting phenomenon does not correlate with integrating sphere haze. Examples of this type of optical defect are occasionally observed in plastic sheet or film samples.
A photometer is described for the quantitative measurement of this type of light scattering. It measures scattered light photoelectrically at a 10° angle with an angular resolution of 1°. It is suitable for plant control applications as well as research and development. Visual estimates of optical clarity correlate well with instrumental low-angle light scattering.
FRED W. BILLMEYER, JR., "Measurement of Optical Clarity by Low-Angle Light Scattering," J. Opt. Soc. Am. 49, 368-371 (1959)