We spend large part of our life in interior spaces that’s why the proper lighting is essential either we are at home or in our workplace because we sense the stimuli coming from the outside world through our eyes. Inappropriate lighting spoils our convenience and makes work more difficult. In order to be able to calculate with lighting in the planning process we have to be aware of the measurements on the surface of the interior space. The target of the thesis is to introduce the basic physical concepts required by the calculation, the methods of planning and counting and the factors of influence of the lighting then creating a model in a MatLab/Simulink environment which is able to determine the quantity of brilliancy in every point of the surveyed room taking into consideration the effects of the artificial and natural light, reflecting lights and shadow effects. By means of our model we are able to determine the optimal arrangement and capacity of the LED lights during the planning process in order to reach the necessary lighting and to plan the costs of the investment and the upkeeps.