It has been experimentally shown that the light trapping due to internal reflection from a smooth surface is reduced as the surface becomes progressively rougher. Although this phenomenon is qualitatively understood well, there has been a lack of detailed analysis of the scattering phenomenon which affects the light emission from thin film phosphors (TFPs). Factors which affect the light emission from the TFPs include electron beam-solid interaction (EBSI), film thickness, microstructure, surface recombination rate, surface roughness, and substrate (thus the interface formed). In many cases, they cannot be varied independently and thus making it difficult to interpret the results quantitatively. Furthermore, as the surface roughness is smaller or same as the wavelength of the emitted light, classical theories based on rectilinear propagation of the light cannot be used without gross simplification. A new theoretical model has been developed by incorporating diffraction scattering at the various interfaces and the factors mentioned above. The model provides an integrated solution to explain the cathodoluminescence (CL) properties of TFPs for field emission displays (FEDs).