SPF protection is not the same as UVA protection. 

UVA rays are the deeper, penetrating rays that are now known as the most dangerous form of UV light coming from the sun. These rays are more responsible for DNA damage leading to aging, wrinkling, and eventually basal cancer cells and/or melanoma. 

UVB rays are the shorter rays that cause reddening of the skin and eventually sunburn. This means that if a sunscreen protects from UVB rays, but not UVA rays, the user will still be susceptible to DNA damage even though no burning occurs.

SPF is the "sun protection factor" which indicates that a product provides 30 times the number of minutes it takes for your skin alone to turn "pink" or "red". For example, that means that a caucasian of European decent who would turn pink in about 15 minutes of direct sunlight without sunscreen - using a SPF 30 sunscreen they should receive 450 minutes of protection - or 7 ½ hours - as prevention from beginning to burn. Therefore, SPF 10 and SPF 100 are supposed to provide essentially the same percent UVB protection for the first 150 minutes - or 2 ½ hours.

3^rd Rock Sunblock is a proven broad spectrum sunscreen lotion that essentially eliminates UVA penetration below the first layers of the skin without providing ANY toxic substances (such as avobenzone - a known endocrine disrupter).