Study on the Perception of High Visibility Level Values

For the development of new lighting functions of modern automotive headlamp systems suitable quality factors are needed to evaluate the driver’s visual performance. The Visibility Level (VL), which compares the contrast of an object with its threshold contrast, has proven to be one of these quality factors. While the perception of small VL values have been extensively investigated, high VL values have not been assessed. Results can help to determine how much light is actually needed to illuminate a situation sufficiently so that vehicles can drive without a loss of safety but at a reduced energy consumption. Here the results of a study in the light tunnel facility of the HELLA GmbH & Co. KGaA in Lippstadt are presented. After the generation of different light distributions, the object luminance is measured and the different VL values of the viewing target are estimated. In the first part of the study a praxis factor for this scenario is determined, which is used for the calculation of the actual VL. The praxis factor equals 10.27. In the second part of the study different light distributions, which create different VL values from 4 to 120, are then shown to and assessed by the study participants. The evaluation shows a saturating assessment of VLs higher than 90. Viewing targets with a VL above this value are all equally described as perfectly visible. A VL above 65 leads to a well visible target. These results are a starting point for upcoming work regarding the generation of new light distribution, such that light will be brought to the streets more adequately.