Public lighting
Visual information is of the utmost importance to road users. In darkness, this information is harder to obtain than in daylight, since human eyes are then less able to discern objects, colours and movement [1] [2]. To support human eyes at times and places when and where natural light sources are not adequate, public lighting may be installed.
In the dark, public lighting enables people to discern the road, other road users and the environment to a sufficient degree. The higher the level of illuminance, the sooner an object is discerned. Moreover, public lighting reduces glare caused by the significant contrast between the headlights of other cars and the dark environment, which is also called headlight glare [3]. Such glare increases the accident risk, in particular for older road users (see the archived SWOV factsheet Visual impairments and their influence on road safety).
Some studies say that public lighting has a positive impact on behaviour. The better the quality of the lighting, the sooner drivers discern intersections and adjust their speed (Rockwell, 1969, as described in Beyer & Ker [4]). Other studies, however, have not proved a difference in speed on account of public lighting [2] [5] and less safe behaviour has also been proved [6].
Vehicle lighting
Activating one’s vehicle lights is important to discern the course of the road and to see and be seen by other road users. Therefore, all vehicle lights should function well and be correctly tuned. Incorrectly tuned lights or the wrong kinds of lights or luminaires could result in glare to oncoming vehicles. Glare arises when the human eye used to a low level of luminance (when it is dark) is suddenly subjected to such a bright light that the eye cannot sufficiently adjust.
The primary function of bicycle lights is to be seen by others. On account of the limited luminous intensity, it is probable that bicycle lights will hardly help cyclists determine the course of the road.
