Contrast of a DIY radial polarizer for locating the Sun

Abstract

Insects utilize the orientation of highly linearly polarized sunlight in the sky as a means of navigation. This mechanism is made possible by the interaction of initially unpolarized sunlight with atmospheric air molecules which creates a distribution of partially polarized light that is symmetric with respect to the position of the Sun in the sky. Taking inspiration from nature, this study aims to construct the appropriate analyzer such that the direction of the Sun is readily determined by viewing through it. We characterized five radial polarizers of increasing thickness by calculating the respective contrast ratios via a circular pixel line scan. Our results show that the contrast ratios of each radial polarizer plateaus at κ̅  ≈ 0.65. We discuss the importance of a high contrast ratio in effectively blocking the orientation of polarized sunlight that corresponds to the direction of the Sun in both clear and obscured conditions.