How Does Sunscreen Filter Out Ultraviolet Radiation?

[FearTheHump]

I am conducting a number of experiments for my Physics EEI, in which UV radiation levels are tested after passing through different types and thicknesses of sunscreens. From what I understand, the basic idea behind sunscreen is that some of the UV rays are reflected/scattered before reaching the skin, while others are filtered to reduce the number of rays reaching your skin.

As part of the investigation I must back my results up with scientific/mathematical evidence, but I can't figure out what quite it is I'm looking for. Any help would be appreciated.

I apologise if this question is inappropriate or in the wrong section.

 

[jbsteele]

A good place to start would be to look at the properties of the sunscreen itself - what type of UV radiation does it filter out, and how effective is it at doing so? You could then use this data to calculate how much of the UV radiation is being blocked and how much is reaching your skin. You could also measure the intensity of the UV radiation before and after it passes through the sunscreen, to gain an idea of how effective the sunscreen is. Finally, you could consider the effect of different thicknesses of sunscreen on the amount of UV radiation that is blocked - does thicker sunscreen block more radiation than thinner sunscreen? In addition to this, you could look at the scientific literature available on sunscreens, to see what research has been done in this area, and what conclusions have been drawn. This can help to provide you with a theoretical basis for your experiment. Finally, you could use mathematical models to estimate the effectiveness of the sunscreen in blocking UV radiation, based on the properties of the sunscreen and the intensity of the UV radiation.