Liquid Crystal Displays (LCDs) are widely used as visualization devices, also in special places and conditions such as: plane cockpits, ''outdoor'' advertisement and information boards, mobile devices, etc. Such applied displays - in relation to standard displays, widely available on the market, should meet special requirements for image quality, such as very high contrast ratio and luminance, wide viewing angle, faithfulness of colour visualization, etc. Additionally, for ''outdoor'' applications, all these parameters should be ensured in high external (sun) illumination conditions. Because an analysis of display parameters based only on experimental results is very difficult, expensive, and long-lasting, a mathematical model of light propagation through the LCD and, based on it, a computer program were worked out. This mathematical model offers determination of optical parameters of a display for any observation angle, any optical parameters of display elements, and any display structure, taking into account the interference phenomena occurring in a display, different directions of ordinary and extraordinary wavevectors and polarization vector, dispersion phenomena of refractive indices and absorption coefficient of the display layers, etc. It should be underlined, that our model takes into account temporal coherence of light and can be used to determine the transmission and reflection coefficients at the same time. Thus, it possible to analyse displays working in transmissive and reflective modes. This paper presents basis assumptions of this mathematical model and our computer program. Additionally, hypothetical results obtained from this program for a display operating under high external illumination are given.