Penrose unilluminable room (original) (raw)

Penrose unilluminable room Roger Penrose's solution of the illumination problem using elliptical arcs (blue) and straight line segments (green), with 3 positions of the single light source (red spot), drawn by CMG Lee. The purple crosses are the foci of the larger arcs. Lit and unlit regions are shown in yellow and grey, respectively. 1 2 3