Spf Test In A Lab I Tested Two Different Sunscreens(SPF 15 And 50) In An Agar Dish With A Yeast Solution...?

In a lab I tested two different sunscreens(SPF 15 and 50) in an agar dish with a yeast solution...? - spf test

I also used to cover an agar plate with foil and it had nothing for them. Aluminum is assumed that higher growth rates will not affect the UV rays through to them? or ought to have less ... Moreover, why some cells do not die on our plates, which are exposed to UV radiation?