Simplified field measurement methods for the CIE mesopic photometry system

For implementation of the mesopic photometry system in CIE 191:2010 to outdoor lighting, two simplified methods to measure the mesopic luminance are proposed. One of the methods, named the Adaptation Spectral Power Distribution) method, assumes that the spectral power distributions (SPDs) of reflected light at test points on the road surface are the same as that of the adaptation field. Another method, named the Source SPD method, assumes that the reflected light SPDs are equal to the SPD of the light source. Error simulations with a real road surface spectral reflectance dataset show that the error distributes over an 8% range due to the variation of the road surface spectral reflectance in the worst case. Although the bias due to the road surface spectral reflectances causes a large error with the Source SPD method, a proposed correction can reduce the error sufficiently. Error simulations also show that the Source SPD method is not so sensitive for lighting scenes that include multiple light source types. It has been shown that the SPD methods can measure the mesopic quantities without scotopic/photopic luminance meters having both V(λ) and V′(λ) detectors when both the adaptation field and test points consist of road surfaces.