The adsorption of Rayleigh particles is analyzed in terms of particle radius and surface coverage with thin island film theory with both scanning angle light reflectometry and ellipsometry around the Brewster angle. A comparison between both techniques shows that an additional uniformity parameter can be extracted out of the experimental reflectivity data. This gives information about the distribution of the adsorbed mass normal to the surface. Fixed angle reflectometry is less sensitive to surface properties than fixed angle ellipsometry. This is closely related to the fact that ellipsometry measurements provide an extra measurable physical quantity, the change in ellipticity at the surface, which has a weaker but different dependence on surface coverage and layer thickness. This enables ellipsometry to distinguish between a broad range of combinations of surface coverage and particle radii that give similar reflectivity. Fixed angle reflectometry can therefore only lead to an interpretation in terms of adsorbed mass. Scanning angle reflectometry measurements, on the contrary, can easily be interpreted in terms of surface concentration and thickness and make further ellipsometry measurements unnecessary.