Abstract
This paper investigates the illuminance needed to detect trip hazards for pedestrians walking after dark. In previous work, it was assumed that the critical obstacle height is 25 mm: further review of accident data and foot clearance data suggests instead that 10 mm is the critical height. Eye tracking records suggest a tendency for obstacles to be detected approximately 3.4 m ahead. Interpretation of obstacle detection data suggests horizontal photopic illuminances of up to 0.9 lux are required for peripheral detection of a 10 mm obstacle 3.4 m ahead, according to the scotopic/photopic ratio of the lighting and the age of the observer.
Highlights
This paper concerns pedestrians and their ability to detect obstacles that might otherwise lead to injury from a fall
It was found that observer age and light source scotopic/ photopic (S/P) ratio affected detection only at the lowest illuminance used in those experiments (0.2 lux).[18,20]
We propose instead that the critical height is 10 mm. This represents approximately the lower quartile of the range of minimum foot clearance measured when walking along a flat surface where hazards are not expected (Table 1) and the lower limit of the range of heights associated with the most frequent number of compensation claims (Figure 2). 10 mm is in the range (8–15 mm) where a change in height has a significant effect of the probability of falling over an unseen obstacle (Figure 3): below 8 mm the obstacle is unlikely to lead to a fall, but above 15 mm it is highly likely to lead to a fall
Summary
This paper concerns pedestrians and their ability to detect obstacles that might otherwise lead to injury from a fall. Thies et al.[16] examined gait characteristics (step width variability, step time and step time variability) when walking along flat and bumpy surfaces (prisms placed underneath a carpet) and they found no effect for the two light levels considered, 47 lux and 927 lux These illuminances are higher than that likely to be encountered on pedestrian footpaths (e.g. the CIE17 recommends average illuminances in the range 2.0–15 lux) and according to the results from Boyce[15] these may already lie on the plateau of performance. In order to improve ecological validity when estimating the light level needed for obstacle detection this article presents a further investigation of pavement obstacles, the critical size as defined by the minimum height of an obstacle likely to lead to a fall and the typical distance ahead the pavement is scanned These data are used to refine the interpolation of the illuminance desirable for obstacle detection
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