Spectral luminous efficiency functions for a ten-degree field in the mesopic range.

Abstract

Mesopic photometry is one of the current problems of the CIE TC-1.4. The luminous efficiency function for mesopic vision has not been established yet, whereas the functions V(λ) for photopic vision and V'(λ) for scotopic vision have been already standardized. In the present study, we measured the spectral luminous efficiency functions in the mesopic range extensively to offer basic data for making photometry more visually meaningful. A direct brightness matching method of 10° field was employed. White light was used as a reference stimulus, and its retinal illuminance was varied from 0.01 to 100 photopic trolands in 0.5 log unit steps to cover the mesopic range. Spectral luminous efficiency function from 400 to 700 nm in 10 nm steps was measured for each retinal illuminance level. Data of seven subjects (19-23 yr old) were collected. It was shown that the function obtained changed gradually from the photopic function to the scotopic one as retinal illuminance decreased. The average and individual variation of seven subjects’ data were presented as basic data of luminous efficiency for mesopic vision. The change of the function due to the different contributions of photopic and scotopic functions was discussed according to the Ikeda-Shimozono’s formula.