Transmittance Calculations of a Sunscreen Film: Considerations of the Coating Geometry and its Probability Density Distribution

Transmittance is an important parameter of sunscreen films such as sunscreen creams, coating materials, sunscreen sheets, etc. Even if the amounts of the sunscreen agent are the same, the transmittance greatly changes depending on the geometry of the coating interface. In this study, we calculate the transmittance considering the coating geometry and the probability density distribution of the thickness of the sunscreen film. We found analytical and numerical solutions of the transmittance in several model cases. It can be used for prediction of performance of the sunscreen film and for a fair comparative evaluation. Mathematical techniques in calculation of the transmittance are also explained in detail.