Figure 3: Lovibond, Joseph W. 1921. Light and Colour Theories and Their Relation to Light and Colour Standardization. London : E&F.N Spon, Limited, 57, Haymarket. Figure from Lovibond, Joseph W. 1921. Light and Colour Theories and Their Relation to Light and Colour. Available at http://rit-mcsl.org/fairchild//lovibond.html