When shopping for sunglasses, before you look for the price tag, there is another tag you need to focus on: the swing tag, which reveals the sun protection factor.
Weighting is also applied to the measurement of sunlight when assessing the risk of skin damage through sunburn, or when assessing the sun protection factor of sun-screen lotions.
Obviously, this approach is very approximate; but such protection factors are deliberately very conservative, and the method has been found to be useful in a deep variety of applications.
