What effect do SPF numbers on sunblock lotions have on their effectiveness of filtering UV radiation?
You can discover this answer for yourself, but Do not use your skin to test the effectiveness of SPF numbers! Instead, use solar active materials. I have found several materials on the Solar Active website that can be used. These include, fingernail polish, shoe strings, tread, and beads. Think About This! The SPF number is suppose to be an indication of how long the sunscreen is effective. To determine this in minutes, multiply the SPF by 10. For example, SPF 30 = 300 minutes (30 x 10), or 5 hours. If SPF 15 is effective for 2 1/2 hours and SPF 30 is effective for 5 hours, does SPF give more protection during the first 2 1/2 hours than does SPF30? The height of the Sun affects the amount of radiation received. If the Sun is really high in the sky the UV radiation received by your skin is greater than when the Sun is lower in the sky. Clues for Investigating (1) I suggest that you place your testing materials so that they receive direct rays from the Sun. You can use a wooden dowel to
