Investigation on angle of incidence and light reflectance

Abstract

Illuminance is a measurement proportional to the intensity of light. When light is incident on a surface, the angle it makes with the normal vector of the surface plane is the angle of incidence. This paper focuses on an investigation of the relationship between the illuminance of reflected light from a glass block and the angle of incidence of the light on the block. By applying Fresnels coefficients, an expression for the illuminance of reflected light is derived in terms of the angle of incidence. The controlled measurements, including the illuminance of s-polarized and p-polarized light of a green laser (532nm), are directly measured to arrive at a set of calculated reflected illuminance at 10 different angles of incidence. The reflected illuminance is also experimentally measured with a light sensor at these angles. Upon the comparison between the two sets of data in this paper, a close resemblance of the shape of their curves is observed, both revealing an increasing reflected illuminance with a growing rate with respect to the increase of the angle of incidence. However, due to some expected systematic errors in the experiment, the calculated data has a generally higher reflected illuminance than the theoretical data at each angle of incidence. Overall, it is confirmed that as the angle of incidence increases, the illuminance of the reflected light increases with a growing rate.