In this module light is incident from one homogeneous medium onto a second one, and the interface between the two media is planar. The incident field can be chosen to be either: (a) a monochromatic completely polarized plane wave or (b) a polychromatic plane wave that is, to a good approximation, unpolarized. In the former case, the user then specifies the amplitudes of the two components of the incident electric field, the phase difference between these components, the angle of incidence, and the wavelength of the light. In the latter case a pre-calculated simulated electric field is used. In both cases, once the incident field has been chosen, the Fresnel equations are used to calculate the reflection and transmission coefficients. The electric field vectors of the light are then displayed at equally spaced points along the incident ray, the reflected ray, and the transmitted ray. As time evolves, the electric fields move accordingly.