In short:
Princeton Consumer Research carried out tests for certification for at least eight sunscreens that fell short of their advertised SPF50 claims in a recent review by consumer group Choice.
Several industry experts have raised concerns about PCR’s testing methodology and calculations.
Both the Cancer Council and the Therapeutic Goods Administration said it was important people continued to use sunscreen as protection against the harmful effects of ultraviolet radiation.
The methodology just makes no sense. I feel like they all should be testing the amount of UV that gets through the sunscreen, not what gets reflected
Whatever is not reflected is transmitted. Where else could the energy go?
It could be absorbed by the material and converted to either
In both cases the wearer is protected from uv, but the the spf will be found to be artificially low.
Both of those would be detected as light coming back, but with different spectra and geometry, so fair enough.