Brightness luminous-efficiency functions for 2 degrees and 10 degrees fields.

CIE V lambda is not representative of luminous-efficiency function based on heterochromatic brightness matching. CIE Technical Committee 1.4 Vision (TC 1.4) presented a 2 degrees brightness-matching luminous-efficiency function based on studies of a total of 31 observers to supplement the V lambda. In view of their importance to illuminating engineering and physiological optics, we analyzed the various conditions under which these seven studies were conducted. Data from three of the groups are considered inappropriate, and we revised the TC 1.4 brightness luminous-efficiency function based on the remaining 19 subjects. Data from 18 Japanese subjects, coming from five research groups, are added to the above subjects, and an averaged luminous-efficiency function is derived. The result does not appreciably differ from the revised TC 1.4 function and is considered to represent a brightness-matching standard luminous-efficiency function for a 2 degrees field. A brightness luminous-efficiency function for a 10 degrees field based on nine Japanese subjects is presented. It differs from the 2 degrees function only at short wavelengths when the functions are normalized at 570 nm. A theoretical approach for using the brightness-matching luminous-efficiency function to assess the brightness of 2 degrees broadband sources is introduced, and some numerical examples are given.