Lighting in residential roads is designed to enhance the visual ability to make interpersonal judgements, which is considered to be a critical task for pedestrians. There appears to be little empirical evidence supporting current standards and consistent conclusions cannot be derived from past studies based solely on facial recognition. This work extends investigation of the relationship between lighting and interpersonal judgements beyond the analysis of facial recognition. The results were used to explore how such data might be used to better estimate appropriate light levels for outdoor lighting.
Analysis of gaze behaviour using eye-tracking suggested that the effect of lighting on interpersonal judgements should be examined using the ‘desirable’ distance at 15 m and a duration of 500 ms: in past studies these have been arbitrary. Two pilot studies carried out to inform the experimental design suggested that (i) recognition of facial features is of particular interest, and (ii) standard facial expressions and body postures did not lead to consistent judgements of intent.
The first experiment collected forced choice judgements of emotion (from facial expression and body posture) and gaze direction after 1000ms exposure under 18 combinations of three luminances, two lamp types and three distances. Better performance was found with higher luminance and closer distance, but with diminishing returns according to a plateau-escarpment relationship. Effect of lamp type was not found in judgements of facial expression, but was found in judgements of body posture and gaze direction for some of the conditions lying on an apparent escarpment.
The second experiment provided further examination of facial expressions under 72 combinations of test conditions: six luminances, three lamp types, two distances and two durations. Luminance and distance were found having significant effect on expression recognition. The effect of lamp spectral power distribution (SPD) was not significant and the effect of duration was suggested to be significant only within the escarpment region of the performance versus luminance.
