Abstract
We present a double-beam method using a spectrophotometer to measure total luminous transmittance and haze. We derived analytical formulas to describe the measurements, which showed the dependence of haze on the exit angle and the reflectance of an integrating sphere. The use of double beams effectively cancels out multiplier factors caused by multiple reflections in the integrating sphere. In contrast, when employing single-beam methods recommended in ASTM (ISO) standards [1-3], the multiplier factors remain present in haze and luminous transmittance measurements. We evaluated measurement uncertainties by propagating the uncertainties of spectral transmittance to those of luminous transmittance and haze. We conducted experiments using two spectrophotometers with different exit angles, which led to different results. For one of the spectrophotometers, which was closer in exit angle to a hazemeter, we compared the experimental results with those obtained from the hazemeter reported in [4,5]. The difference in haze from the ASTM (ISO) method was 1.3 % (0.2 %) in the haze unit, and total luminous transmittances agreed with each other within their uncertainties. These comparison results were consistent with the theoretical predictions. Additionally, we calculated haze changes with varying exit angles to interpret the observed differences between the two spectrophotometers.
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