Transmittance vs Absorption Curve

Sometimes you will see transmittance of absorption curves to show the UVA and UVB protecting abilities of a sunscreen active. Transmittance is the fraction of incident light at a specified wavelength that passes through a sample. In other words it measures the amount of wavelength that goes through. You want the transmittance to be low for a sunscreen active because that shows that low amounts of wavelength are passing through the sunscreen active. We want UVA and UVB to be absorbed and scattered, not to pass through and penetrate our skin. The transmittance curve below is that of a ZnO sunscreen. We see fairly low transmittance of UVB and UVA radiation. On the other hand, we see a high transmittance of visible light which is showing that ZnO is not very whitening. If ZnO scattered a large amount of visible light then it would be very whitening and ashy looking on the skin.

Typical UV protection provided by ZnO Sunscreen Credit Link

If we flip this curve, we get an absorption curve which is the opposite of a transmittance curve. An absorption curve shows the amount of wavelength being absorbed, not transmitted. For a sunscreen active, we want a high amount of absorption of UVA and UVB radiation because that shows it will not penetrate the skin and cause damage.

Transmittance and absorption curves are important to understand the UVA and UVB protecting of the sunscreen actives that you will be working with.