Fig. 20 Structure of integrating sphere
As shown in Fig. 21, when the reflection spectrum of a sample (blue line) is measured, it sometimes has an unexpected shape (red line). In most cases, this is caused by a dirty reflectance standard white plate or integrating sphere. In the case of a dirty reflectance standard white plate, the reflectance particularly in the ultraviolet region decreases. If such a plate is used as a reference, the reflectance measured for a sample will be abnormally high.
Fig. 21 Example of abnormal sample spectrum (red)
Fig. 22 Spectra of dirty white plate (red) and new white plate (blue)