Automatic measurement of spectral bidirectional transmittance distribution function on translucent optical materials

A measurement platform of spectral bidirectional transmittance distribution function (BTDF) with a full three dimensional spatial coverage is developed based on a fiber spectrometer, a tungsten-halogen lamp and a 3D mechanical rotation angle system. The measurement software and the control software are integrated to realize the automatic measurement. The measurement equipment has a broad spectral coverage, a large angle range, a wide dynamic response and a short acquisition time. The measured spectral range is 380-760 nm with 0.04 nm spectral resolution. The measured angle range is 0-80° in zenith angle and 0-360° in azimuth angle with 0.01° angle resolution. The dynamic range is 10⁷ and the minimal integration time is 1 ms. The measurement of spectral BTDF on translucent frosted glass is performed and a large amount of measured data is obtained with the measurement error no more than 3.28%. It provides a reliable description facility for spectral and spatial transmission characteristics of the translucent materials.