1) IEC 60417: Graphical symbols for use on equipment, International Electrotechnical Commission (Geneva), http://www.graphical-symbols.info/equipment (2002)
2) ISO/IEC 80416-3: Basic principles for graphical symbols for use on equipment - Part 3: Guidelines for the applications of graphical symbols, International Electrotechnical Commission in Geneva (2002)
3) International Electrotechnical Vocabulary, IEC/CIE 60050-845: Lighting, http://domino.iec.ch/iev
4) L. A. Olzak and J. P. Thomas: Seeing spatial patterns, In: Handbook of Perception and Human Performance, Vol. 1, Chapter 7, John Wiley & Sons (1986)
5) A. A. Michelson: Study in Optics, University of Chicago Press (1927)