An Alternative ESI System Based on Human Visual Acuity

Abstract

An alternative ESI was derived directly from the empirical relationship among visual acuity, background luminance, and contrast. This quantity (ESI(V)) was defined as “the equivalent illumination under the reference lighting condition which gives the same visual acuity as that produced by the real lighting condition.” It was shown that relative value of ESI(V) was uniquely related to CRF and was independent from the level of raw illuminance. Second, the variation in ESI(V) at different positions within a room was not as large as that in the current ESI system. The origin of these features and the limitation of ESI(V) was discussed.