Abstract
The CIE mesopic photometry system (CIE, 2010) was based on target detection performances at an eccentricity angle of 10 degrees. It has not been confirmed whether the MES2 system can be applied to other eccentricity angles in the peripheral visual field. To verify the validity of the CIE mesopic photometry system and modify the system if necessary, this study conducted a target detection experiment by employing six subjects. This experiment measured the subjects' reaction times for targets presented at eccentricity angles of 5, 10, 15, and 25 degrees from the center of the visual field. This experiment used light levels between 0.005 cd/m2 and 2 cd/m2 and two lamp spectral power distributions of yellow LED (S/P ratio=0.10) and white LED (S/P ratio = 1.86). Based on the results of the experiment, this study found that the visual field within 5 degrees from the center of the visual field can be treated as the central visual field where only cones function even under mesopic light levels. The CIE mesopic photometry showed good correlations between mesopic luminances and reaction times for the two SPD conditions at eccentricity angles of 10 and 15 degrees. However, the luminance borderline between the photopic vision and the mesopic vision at the eccentricity angle of 25 degrees seemed to be higher than 5 cd/m2, which the CIE MES2 defined.
Therefore, this study attempted to modify the mesopic luminance formula only for the eccentricity angle of 25 degrees.
