This is important.
Sunscreen SPF numbers are not well understood by the public. People associate SPF numbers radiation protection and mistakenly think that the highest number means more protection. The SPF numbers actually are associated with time as well as protection. While an SPF 30 blocks 98% of radiation, it also indicates that if your skin would normally become red in 30 minutes, using an SPF of 30 would allow you to stay in the sun an extra 30 minutes.
People should know what they are paying for. Most of the time lowere level sunscreens are not cheaper than higher SPF suncreens, but it cases where there is a significant price differnce, this is important to know. It is also important to know how much SPF you need and how long it takes to wear off.
The SPF measuring system for sunscreen is not very transparent: SPF 15, SPF 30. Therefore, the government should require that sunscreen manufacturers disclose on the bottle the product's effectiveness based on percentages. In other words, SPF 15 blocks 93% of incoming radiation, while SPF 30 blocks 97%. Sunscreen manufactures should simply disclose the percentage of incoming radiation that the product blocks, instead of the confusing SPF scale.
SPF on sunscreen is a joke. People believe that the higher the number creates such a difference in protection but it really doesn't. If companies are allowed to number their products with 50 vs 30 yet only provide a 1 percent difference it should be clearly labeled and marked to prevent a false sense of security with the consumer.