Influence of spectral power distribution and photometry on contrast gain in mesopic illumination conditions

Abstract

The different levels of night-lighting activate adaptation mechanisms such as contrast gain. The influence of different spectral power distributions on this mechanism is analyzed. In addition, two photometry systems are evaluated in terms of luminance effect on contrast gain. A two-channel Maxwellian optical system was used to obtain contrast gain values of thirteen young subjects at 10º of temporal retinal eccentricity. High-pressure sodium and metal halide streetlamps provided a background luminance of 0.01 cd/m2. A luminance meter provided a photopic measurement of luminance and a MES2 photometry system was used to mesopic luminance calculation. Contrast gain is significantly lower for sodium lamp using photopic photometry. However, mesopic photometry is responsible for an increase in background luminance for sodium lamp, improving contrast gain and leading to the absence of differences between lamps. Thus, spectral power distribution influence on contrast gain depends on the photometry system employed.