Abstract: Elliptically polarized light and partially polarized light show similar change in light intensity through a rotatable,so it is difficult to differentiate them.Application of two 1/4 wave plates in the path of elliptically ploarized light and one 1/4 wave plate in the path of partially polarized light is a way to distinguish them from each other.The experiment results showed that the intensity of partially polarized light changed with no extinction phenomenon，but the intensity of elliptically polarized light changed with the extinction phenomenon,and the elliptial polarized light changed into shallow polarized light through 1/4 wave plate.

Key words: elliptically polarized light, partially polarized light, polarizer, 1/4 wave plate