The paper reported a method to characterize the retardance of retardation films at different wavelength. The system is based on the method of rotation of quarter wave-plate. A spectrometer was sued as the light source

color filters and a photodetector. We measured some samples using the system

analysed the measurement data

and obtained the spectrum characteristic of the retardation films. According to the theory of the system

the variation of the light source and other errors related to light intensity are not so critical for the measurement in this system. Furthermore

some quarter wave-plate’s affect for the other wavelength is very little

so the retardance is determined in a high accuracy and in a high repeatability. In principle

any retardance within the system accuracy can be measured.