As a simplified view, light is incident upon a sample, three processes occur: transmission, absorption, and reflection, as schematically shown in the follow figure, including retroflection, diffuse reflection, specular reflection, diffuse transmission, and specular transmission.
A more detailed view of the process can be shown in the following figure.
Transmittance, haze, and clarity for plastic films can be measured according to ASTM D 1003, where haze is the percentage of light that deviates from the incident beam by more than 2.5° on average. Clarity is evaluated at angles of less than 2.5°. Source of the figure: BYK
Transmittance and haze are calculated by the following equation (source: ASTM D 1003 description):
