Updating this post to add a bit more context. This graph is based on one from Critical Wavelength and Broad-Spectrum UV Protection by Dr. Dembny. Critical Wavelength (CW) is a standard used by the United States FDA to determine if a sunscreen can be deemed “broad-spectrum”. Wavelengths ranges correspond to different types of UV waves: wavelengths 280 nm – 320 are UVB, 320 nm – 400 are UVA. Broad-spectrum sunscreen aims to protect against UVA and UVB rays. The CW is calculated by looking at how much UV is absorbed by the sunscreen at different wavelengths. The CW is calculated by figuring out the area under the full curve, and then determining how far to the right on the x-axis you can go to account for 90% of the area under the curve. This point on the x-axis is the CW. If that CW is greater than or equal to 370, the sunscreen is broad-spectrum, and provides sufficient coverage from both UVA and UVB rays.
Here is the figma doc where I threw some notes and links to the resources I looked at: https://www.figma.com/file/Ws8WkXzwuJcjSXYfbOQ4hE/Daily-Pracitce–Day-6?node-id=0%3A1