Due to all the effects described, the absorbance curves A(l)
recovered by the measurement of the substrates with and without
the sunscreen were very different among them both in shape and
absolute value. For these reasons, absorbance and reflectance
measurement curves are not meaningful by itself for labelling,
unless they are used to calculate parameters that correlates to in
vivo measurements or they are used only to make a relative
comparison between different products. Generally, the trend
among different SPF products was maintained, except in the case of
the product labelled SPF 20 when applied on Transpore (Fig. 8a)
and product labelled SPF 15 when applied on PMMA (Fig. 8d). In
these cases, the transmittance curves intersected those of products
with higher or lower SPF values.