NBS reference hazemeter: its development and testing

A research hazemeter has been developed by the Radiometric Physics Division of the National Bureau of Standards for the quantitative analysis of light scattering by optical materials. The instrument is designed to measure percentage haze as set forth in the prescribed conditions recommended in ASTM Test Method D 1003. The hazemeter has several special features which make it possible to vary the geometrical conditions of the collimated light beam and the integrating sphere detector system for detailed studies of light scattering. Light scattering associated with the instrument source and collimating optics has been reduced to less than 0.1% of the total light beam by using a diffraction limited off-axis parabolic mirror to collimate the hazemeter light beam. The source optics provide a collimated light beam of approximately 6800 K. The detector is a silicon cell photodiode with a V(lambda) window. This combination gives the system a response corresponding to the visual luminosity function. The detector nonlinearity and instrumental errors associated with the accuracy of the integrating sphere geometry have been analyzed. The over-all uncertainty in percentage haze has been reduced to +/-0.2%, and light scattering of less than 0.5% can readily be measured.