The illuminance distribution at certain points in the room can be calculated using the inverse square law. This is based on the fact that the illuminance reduces with the square of the distance from the light source. Indirect lighting components are not included in this calculation. Point illuminances can be calculated for a single luminaire or several luminaires. For confined areas with individual luminaires, manual calculations can be appropriate. Where there are a number of luminaires and functional areas in a room, designers use lighting design programs that then include the indirect lighting components. The programs can determine the illuminance for all room surfaces and working planes. The results are displayed in graphic representations of Isolux charts or false colour diagrams.