The adsorbance values give the respective transmitance values spanning from 0.001 up to 0.99 (0.1-99%). In order to record correctly the low values, it is essential to use a spectrophometer with an high dynamic range,as the case of a double monochromator system. The absorbance values A (&), and equivalently,the PF values showed a high degree of vatriation among subtrates. This result is consistent with several studies. Pearse and Edward, using human stratum corneum and Transpore as substrates for SPF evaluation . observed that in 10 out of 11 sunscreens studied the SPFvalues measured with Transpore were systematically higher than those obtained using human stratum corneum. In another study. Lott et al. Adopting there different substrates obtained significant differences in the SPF values; these results have been related to the non-uniformity of product application. Other physical effects related to the coupling between substrate and sunscreen can partially for such discrepancy . As suggested by Ferrero et al. Who showed a correlation between substrates roughness and SPF outcomes in case in of PMMA plates.
We have analyzed the variability in term of absorbance values dy using different substrates as follow.