我这里有一篇论文，研究了海边防晒伞与SPF100防晒霜防护力的对比。直接跳到结论就：This is the first clinical study, to our knowledge, to directlyevaluate the efficacy of protection against UV rays of a beachumbrella and compare it with that of a high-SPF sunscreen ina side-by-side trial. Umbrella shade alonemay not provide sufficientsun protection during extended exposure to UV rays.Although the SPF 100 sunscreen wasmore efficacious than theumbrella, neither method alone prevented sunburn completelyunder actual use conditions, highlighting the importanceof using combinations of sun protection practices to optimizeprotection against UV rays.
简单翻译一下：在长时间暴露于紫外线的情况下，单独使用遮阳伞不能提供足够的紫外线防护。与此同时SPF100的防晒霜防护力要优于遮阳伞。两者都不能完全阻止晒伤，这体现了联合使用多种防晒措施对于紫外线防护的重要性。