The purpose of this study is to determine the area of light emitted by a source in an orthogonal polygon on a two-dimensional lattice using the cellular automata construction method. By applying this method, an efficient algorithm was tested and developed to determine the area of light propagated. The algorithm, although not optimal, gives a close approximation of the number of cells on the lattice that are to be illuminated. Furthermore, the algorithm acknowledged in this research is sufficient to work with any orthogonal polygon. This research is based on a classical computational geometry problem – the art gallery problem. It is hoped that the results of this research can contribute to finding more efficient solutions to the problem as well as other computational geometry problems.