Spectral luminous efficiency as a function of age

Spectral luminous efficiency function for a 2-deg field at a photopic level (100 Td) was measured for 91 observers by flicker photometry (FP) and for 97 observers by direct brightness matching (DBM), to find age-related chang e in the efficiency function as well as to obtain a reliable data set to be used in photometry. Observers ranged in age from 11 to 78 years. A gradual reduction of luminous efficiency with age was observed for both functions by FP and by DBM in the short-wave region, which was expected because of th e age-related increase of optical density of eye lens. A similar age-relate d reduction of efficiency was observed in the long-wave region for the func tion obtained by DBM; this reduction was regarded as being due to reduced c hromatic contribution to brightness with age. Principal components analysis on the spectral efficiency data and an analysis of the efficiency differen ce between the data obtained by DBM and FP confirmed this conclusion. Assum ing a log-linear change in efficiency with age for any wavelength throughou t the life span, spectral luminous efficiency function at any age was deriv ed for photometric use. (C) 2001 Optical Society of America.