Indoor visual comfort is one of the leading requirements for building design. Results of computer daylight simulations serve to optimise the design process. Computer programs Ecotect and Radiance were used for the simulation of daylighting from tubular light guides of various diameters and lengths. The internal illuminance calculations were compared for two extreme situations in boundary conditions - sunny summer sky and winter overcast sky, determined for the climatic region of Central Europe. Daylight simulations give information about indoor illuminance on vertical and horizontal reference planes depending on various dimensions of the light guides. Finally, the assessment of annual variation of average internal illuminance from light guides under different outdoor climatic conditions - for uniformly overcast sky, intermediate sky, clear sky and sunny sky - was completed. The simulation results serve to evaluate daylighting and visual comfort in interiors illuminated from light guides.