| ▲ | parineum an hour ago | |
It's contextual depending on which end of the probability is the desired outcome. SPF is like this. SPF 30 allows 1/30th (3%) of the UV through it, blocking 29/30ths (97%). SPF 50 (2%) allows 1/50th, blocking 49/50ths (98%). Using the denominator, in this case, expressed the efficacy much more intuitively. Comparing SPF 30 vs 50 better expresses the increase in efficacy than 97% vs 98% does. One could also express it as the amount that passes the filter but it is Sun _Protection_ Factor not Sun _Transparency_ Factor. | ||
| ▲ | jrowen 8 minutes ago | parent [-] | |
On the other hand, it's completely unintuitive that "Sun Protection Factor 30 = 1/30th of UV light passes through it", and I had no idea there was any correlation there before this comment. The only intuitive bit about that system is "bigger number does more." | ||