Relative spectral luminous efficiency function of 2° and 10° fields determined by flicker photometry and direct heterochromatic brightness matching

Abstract

With a view to developing a new photometric system which will give a better agreement with the visual impression of the Iight, the effects of both the visual field sizes and the criteria for measurement of spectral luminous efficiency functions on the shapes of the functions were examined in the case of 2° and 10° fields, by applying two different methods, flicker photometry and direct heterochromatic brightness matching, using the same white reference. A 2° field function by flicker photometry was very similar to Judd's modified V(λ) function while a 2° field function by direct heterochromatic brightness matching showed hilly humps on both sides of 570 nm. A 10° field function by flicker photometry showed no significant differences from both the CIE ȳ10(λ) and the ETL ȳ10(λ) functions derived from the color matching functions. These findings suggest that the CIE ȳ10(λ) function should be used as a standard photometric observer in the large visual field. A 10° field function by direct heterochromatic brightness matching showed the largest values among the four relative spectral luminous efficiency functions over the whole range of visible wavelengths. The relative spectral luminous efficiency data obtained by heterochromatic brightness matching for the 2° and 10° fields here will provide data useful for development of a new photometric system where a great importance is to be attached to a correspondence between sensation of brightness and photometric quantity. © 1985, The Illuminating Engineering Institute of Japan. All rights reserved.