A novel apparatus was used to examine the effect of light source, illuminance and observer's age on the ability to detect obstacles in peripheral vision, simulating a raised paving slab under mesopic visual conditions. The data collected were used to determine the height of obstacles above the paving surface required for 50% detection. From these detection heights it was determined that: (1) obstacle detection was influenced by illuminance, the 50% detection height being lower at 20 lux than at 0.2 lux, (2) the young observers (545 years old) showed the smaller 50% detection height at 0.2 lux, but at 20 lux there was no difference in obstacle detection height between the younger and older (460 years old) age groups, and (3) obstacle detection was affected by lamp type at 0.2 lux, with the 50% detection height decreasing as lamp S/P ratio increased, but at 2.0 and 20 lux there was no significant difference between the three test lamps.

This paper investigates the critical visual tasks of pedestrians, the first step in a review of design guidance for lighting in residential roads. Eye tracking was used to record pedestrians' visual fixations when walking outdoors in daytime and after dark with a concurrent dual task to better understand which fixations were critical. Fixations at critical instances, these being shown by slow reactions to the secondary task, were categorised into one of eight groups. Of these, the path and other people were the most frequent items, with people more likely to be fixated at a far distance and the path at a near distance. After dark the path was more likely to be fixated and other people less likely to be fixated compared with daylight.

This paper reports on experimental work carried out to test metrics for predicting spatial brightness at mesopic levels under lamps of different spectral power distribution. The side-by-side matching technique was used following an extensive review of experimental design. Five different types of lamps were presented in all 10 possible pairs, these being selected to compare brightness predictions based on established characteristics of lamp spectrum such as colour rendering index, correlated colour temperature and the scotopic/photopic ratio. The results were also used to test proposed systems for predicting brightness and visual performance at mesopic levels. Of the lamp characteristics examined the scotopic/photopic ratio exhibited the highest correlation with the test results. The new CIE recommended system for visual performance based mesopic photometry was found to give an acceptable prediction of the brightness results.

British Standard BS5489-1: 2003 permits a trade-off between colour rendering and illuminance for lighting in subsidiary streets—if lamps of high colour rendering index are used, such as metal halide instead of low- and high-pressure sodium, a lower illuminance can be used. A series of tests are carried out to validate the trade-off and this paper reports on the new brightness data from these tests. The experimental results support the trade-off but it is suggested that its application may depend on the stage of chromatic adaptation at which the assessment of brightness is made. The experimental results are compared with predictions made by four models of mesopic photometry.

Obstacle detection is an important visual task for pedestrians. An experiment was carried out to measure the ability to detect peripheral obstacles under variations of illuminance and scotopic/photopic luminance ratio and with older and younger test participants. The LED array used in this work enabled scotopic/photopic ratio to be varied whilst chromaticity was held constant. The tests employed a full-scale model with dynamic fixation and walking to better simulate pedestrian experience than in past work. Detection performance increased with illuminance, reaching a plateau at 2.0 lux. A higher scotopic/photopic ratio improved obstacle detection but only at the lowest illuminance used in this study (0.2 lux). Older participants showed poorer obstacle detection performance than younger participants but again only at the lowest illuminance.