The Unobstructed Reflection Model (Young Theory) for calculating light scattering from a spherical particle on a smooth surface is reviewed and presented with special attention to the polarization of the incident beam and position of the detector. As a test of the approximation,some calculations for 0.54μm diameter polystyrene latex spheres (PSL) on a silicon wafer is carried out. The results of these tests are presented and compared with experimental results that published abroad previously.