In this work, the accurate light-generation model which accounts for t
he wave nature of light is compared to the classical model which assum
es the simple exponential decay of absorbed light and considers only t
he two most important reflections. Both models are used to calculate b
oth internal and external electrical characteristics of the illuminate
d amorphous silicon solar cell. The results are compared to find out w
hen the classical formula can be used, and when accounting for light i
nterference is necessary.