Patent US 4,177,579

A simulated view on a viewing surface of a raster scan television display of a changeable illuminated area located on a plane surface is provided. The source of illumination is a cone of light whose apex can be located at any distance from an eyepoint and the plane surface and whose conical surface intersects the plane surface creating the illuminated area. Electronic components determine when a line of sight from the eyepoint through the viewing surface intersects the illuminated area. For each line of sight intersection point lying within the illuminated area, a corresponding illumination is created on the viewing surface.