Determining Sunscreen Efficacy in the Ultraviolet Range

The Grizspect team has designed and constructed an ultraviolet solar spectrograph to investigate the efficacy of active ingredients found in chemical and physical sunscreens for blocking UV-A (320-400nm) and UV-B (290-320nm) light. Incoming sunlight is collimated and reflected onto an aluminum-coated diffraction grating. We place an ultraviolet-sensitive camera in the 280 to 400 nanometer range of diffracted light to measure and record the intensity of light incident at each wavelength, constructing a transmission spectrum. Sunscreen is then applied in a uniform layer onto a fused silica slide and placed at the initial aperture of the instrument. We examine spectra filtered by each of the four sunscreens and one control, consisting of the silica slide alone. The results of our experiment reveal which active ingredients most effectively filter UV-A, UV-B and UV-C light, as well as ultraviolet light as a whole. With an SPF rating system that is minimally regulated, our findings are essential for holding sunscreen distributors accountable in their advertising claims. The Grizspect team is competing in the National Student Solar Spectrograph Competition at Montana State University in May for their instrumental design, construction, and data acquisition