In this paper the authors investigated the process of reflection of a flat plate collector is to be studied. As the behavior of the performance of solar collectors is depending on a lot of factors, among them on the wavelength of the sun light, reflected solar radiation. Based on the measurements an analysis was carried out to determine the rate of scattered radiation. Incident irradiance on a non-horizontal surface from a variety of incident angles may cause the reflectivity to change. Assumptions about the reflectivity of vertical surface are frequently made for a variety of purposes but are rarely quantified. The paper introduces the result of the measurements and the analysis.