Use of bidirectional transmittance distribution function measurements to determine transmittance haze

Abstract

Accurate and traceable measurements of transmittance haze are required for quality control in various different industries, such as optoelectronics, automobiles, and agriculture. Transmittance haze is defined as the fraction of light transmitted through a material that deviates from the incident beam by more than 2.5∘. Various documentary standards specify the use of an integrating sphere with a prescribed geometry for the measurement of transmittance haze. This paper uses goniometric measurements of the bidirectional transmittance distribution function (BTDF) to calculate transmittance haze according to the definition and demonstrates that the sphere-based realisation of transmittance haze specified in the documentary standards does not agree with the definition, with the difference being up to 20% for some samples. The BTDF measurements are also used to simulate the integrating sphere haze, allowing the sensitivity of the sphere haze to errors in the integrating sphere geometry to be calculated.