8 and in detail for selected sunscreens
(SPF 4 and 12) in Fig.
10, the absolute value of the absorbance vary
considerably among substrates; this is also because, according to
what explained, the amount of back reflected radiation with
respect to the transmitted radiation is very different. Besides these
physical aspects related to surface/volume scatting of light,
another fundamental event that can affect the result is the
different chemical interaction of sunscreen with substrate
materials. A further possible physical effect that can justify the