Suspended particle devices (SPDs) constitute an electrically powered chromogenic technology, in which the active layer quickly are able to rapidly switches from a dark bluish-black dark color state to a clear greyish color appearance when an AC electric field is applied. Two-flux and four-flux models were used to derive refractive indices and extinction coefficients, as well as scattering and absorption coefficients, of the particle-containing active layer. These entities were used in model calculations to predict the direct, total and diffuse components of the transmittance andthe reflectance, together along with the color appearance and haze, as a function of the thickness of the active layer. An optimum thickness for the optical contrast of the SPD was determined in this way and was found to be in the range of 200 to 300 nm. The SPDdevices device exhibits a significant reflectance haze particularly in reflection.