A Novel Fluorescent-Material-Based Simple Method for Sunscreen Evaluation

ISO standards exist for evaluating sunscreens, such as those based on visual inspection. This assessment yields subjective results and is thus unreliable. Therefore, to verify the results of the visual assessment of sunscreens, quantitative evaluation methods are necessary. These methods require the measurement of the total radiation energy that is diffusely transmitted in all directions. For the measurements, although an integrating sphere is widely used to measure diffusely transmitted radiation, a simpler measurement would contribute to the easy usage of quantitative and objective evaluation. We propose the use of fluorescent materials as an alternative method to characterize sunscreens. In this method, a layer containing a fluorescent material is placed behind the sunscreen, and when the excitation radiation transmitted through the sunscreen reaches the fluorescent layer, it emits fluorescence. The feasibility of this measurement method was evaluated through numerical analysis and it demonstrated that hemispheric transmittance can be measured when the fluorescent layer is of high concentration or thick. Additionally, a prototype fluorescent layer was fabricated, and also the results were compared with the amount of diffusely transmitted UV from several commercial sunscreens. This pilot evaluation measurement method showed that the UV shielding index shown on the package does not necessarily truly reflect the amount of UV energy transmitted through the sunscreen, thus failing to provide the expected protection.