Example of Reflectance Measurement Using Integrating Sphere: Difference of Spectra Depending on White Reference Plate

Introduction

An integrating sphere is generally used in measurements of the reflectance of samples which display scattering or diffuse reflectance, such as solids and cloudy liquids. An integrating sphere is spherical in shape with an inner wall made of barium sulfate or some other light-scattering material with high reflectance, and has the effect of causing light that enters the sphere (measurement light) to scatter uniformly. This enables highly accurate detection of transmitted light or reflected light from the sample, even when measuring samples with scattering properties. Because the reflectance of samples obtained by measurements using an integrating sphere is a relative reflectance value obtained by comparison with the white reference plate as a standard, the obtained value depends on the reflectance of the white reference plate. Therefore, the measured reflectance of a sample may change if a different white reference plate is used, or if the reflectance of the white reference plate changes due to deterioration, even when using the same plate. Although pressed and solidified barium sulfate (BaSO4) is generally used in white reference plates, other substances are also used, including aluminum oxide (alumina, Al2O3) and magnesium oxide (MgO) powders or a fluoropolymer white reference plate with a specified reflectance. This article introduces an example in which the reflection spectra of various samples were measured using a UV-3600i Plus ultraviolet-visible light-near infrared (UV-VIS-NIR) spectrophotometer and ISR-603 integrating sphere attachment in order to verify the effect on sample measurements in case barium sulfate and magnesium oxide powder reagents and a fluoropolymer white reference plate are used in the white reference plate.

January 26, 2021 GMT