A computer system for calculating the illumination on coal mine surfaces due to machine-mounted lights is described. Utilizing numerical models of mining machinery and measured data on luminaire output characteristics, the program computes the foot-candle levels incident on the mine entry surfaces for any desired machine- luminaire-entry configuration, and shadowing effects of the machine are taken into account. Results are provided at 2-foot intervals on the face, left and right walls, floor, and roof. The system operates, interactively from a tektronix 4014 graphics terminal which handles all input-output functions. The software is installed on a cyber 74 computer that communicates with the terminal by a telephone line.