Re: The project I am proposing is the testing of different

Dear user,

The simplest suggestion would be a photo cell with a filter cutting off
all but the ultraviolet part of the sun spectrum. Applying a thin film
of the sun block (take care to be precise in film thickness) and
measuring the yield of electricity or other characteristics of the cell ,
one can get a rough estimate. Another variant would be a piece of photographic
paper with the same filter and a layer of sunblock.

Some sunblocks work on a different principle then just filtering off
the  UV radiation. For these one can only suggest a suitable
biological model such as human skin. Apply a number of sunblocks, expose
the skin for a measured length of time, when the tan develops, take a
picture of the skin area and estimate or measure the darkening of the 
different areas. Take care not to burn yourself.

HiH.

A.G.E.