We have analyzed the variability in term of absorbance values
by using different substrates as follow. Let’s try to design the
interaction between two media, A (sunscreen) and B (the
substrate), and light taking into account different physical effects.
If the two media have both smooth faces and low scattering
properties, the transmitted radiation path is straight forward while
part of radiation is straight back reflected (Fig. 9a). If medium A is
diffusing, both the in-coming radiation and the back reflected at
interface are then scattered in all directions, and part of the last one
is again re-directed in the substrate (Fig. 9b); if the substrate has a
roughened surface, as in case of PMMA plates and roughened