The V(?) function accepted in 1924 is valid for photopic vision. It was long recognized that for para-foveal vision this function does not describe luminance perception correctly. In 1964 the CIE accepted a large field colorimetric observer, but this system had no photometric counterpart. Subsequent research has shown that y10(?) function can be used as the spectral luminous efficiency function of a 10° photometric observer. The present report provides guidance when and how this large field photometric observer could be used, especially if luminance has to be determined para-foveally. Based on the detailed evaluation of the available literature data TC 1-59 came to the conclusion that the adoption of a 10° photopic photometric observer [V10(?)] can be recommended to the CIE and that this system should be based - according to the original recommendations of the CIE Colorimetric Committee - on the y10(?) function of the CIE 1964 standard colorimetric observer.