by the 1960s, it was realized that cones in the human visual system covered a larger field of view than previously believed.the visual matching experiments were repeated by w. s. stiles, j. m. Burch and N. I. Speranskaya using this wider field of view and in 1964, the Cie 10° standard observer was published. the 10° standard observer is recommended as best representing the spectral response of human observers. as shown in Figure 2, the 1931 2° standard observer is similar to the 1964 10° standard observer and was not discontinued with the 1964 release due to its incorporation in many industry product specifications. Today, the 1964 10° standard observer is recommended by the Cie as appropriate for most industrial color applications but the 1931 2° remains available as a measurement choice. the relative sizes of the two f ields of view are shown in Figure 1.