A Grid in Perspective for Road Lighting Calculations

ABSTRACT In road lighting, calculations are made within the rectangular CIE grid while measurements conducted with Imaging Luminance Measurement Devices (ILMD) have a trapezoidal shape. We propose to build a grid that takes the observer’s perspective into account by projecting ellipses of adjustable dimensions than can match human vision or ILMD angular aperture and allow direct comparison with luminance images. Lighting standard criteria definitions remain unchanged and values of average luminance and longitudinal uniformity are equivalent. However, as the grid in perspective describes more finely the luminance distribution, the overall uniformity is lower than in the classical grid but more representative of observer’s perception. We present in detail our approach, give the corresponding code, expose calculations performed with this new grid and show an example of direct comparison between calculations and measurements.