This study looked at a sample of street lighting installations spread over the urban areas of nine territorial local authorities. Standard street lighting parameters were measured in the field using a variety of instruments including illuminance meter, luminance meter and a calibrated digital camera.
Field measurements were related to the ratio of night-time to day time crashes (from the CAS database) as a measure of night time safety vis-a-vis daytime safety. This index makes use of the fact that road lighting only influences night time crashes. Also as it measures relative rather than absolute crash frequencies it was possible to include non-injury as well as injury crashes to substantially increase sample size and sensitivity.