SPECTRAL SENSITIVITY AND ADDITIVITY OF DISCOMFORT GLARE UNDER STREET AND AUTOMOTIVE LIGHTING CONDITIONS

An experimental apparatus (glare booth) was constructed to study the effect of spectral power distribution of light sources on discomfort glare (DG) perception and its visual mechanisms. The glare booth included a 0.1 cd/m(2) mesopic adaptation background (S/P=2.1) and two quasi-monochromatic (QM) optical channels providing a variety of QM and quasi-bichromatic (QB) glare sources to investigate spectral behaviour and spectral additivity of DG sensitivity. Adaptation level and observation geometry (0.3 degrees glare source at 4.3 degrees off the visual axis) addressed practical applications of automotive headlamps and street luminaires. Absolute DG sensitivity was quantified as the reciprocal value of radiance in the direction of observation. Relative spectral DG sensitivity was interpreted in terms of retinal (L+M), rod, S and chromatic (vertical bar L-M vertical bar) mechanisms suggesting rod and chromatic contribution in addition to (L+M). Chromatic signals of QM results imply non-additivity. QB results were not conclusive. Both absolute and relative spectral sensitivities exhibited large inter-observer variability.