I thought this was interesting. It would seem that SPF only protects against UVB rays and you need to look out for specific UVA filters
http://uk.news.yahoo.com/pressass/20080801/tuk-half-of-suncreams-lack-protection-6323e80.html
http://uk.news.yahoo.com/pressass/20080801/tuk-half-of-suncreams-lack-protection-6323e80.html