2. Basic Lighting Quantities

The first thing to determine is which are the lighting parameters that positively influence the visual performance and comfort of the users of road lighting. For this it is necessary to define those basic lighting quantities that play a dominant role in the seeing process of motorists, pedestrians and residents, namely: illuminance or luminance. For motorized traffic it is the luminance of the road surface that forms the background to possible objects on the road. For the normal directions of view of motorists, the reflection properties of road surfaces, needed for the determination of road-surface luminance, can be photometrically characterized. Therefore, road surface luminance can and is indeed used as the basic lighting quantity for road lighting for motorized traffic. Since the directions of view of slow-moving traffic such as pedestrians and cyclists are more varied and the reflection properties of surfaces of interest are widely different, we have to fall back on illuminance as the basic lighting parameter for road lighting specifically meant for non-motorized road users. The basic measure here for the lighting of the road and pavement is the horizontal illuminance; for the lighting of facades it is the vertical illuminance and for the lighting of faces of persons in the street it is the semicylindrical illuminance.