Lighting for subsidiary streets: investigation of lamps of different SPD. Part 1—Visual Performance

Abstract

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 such as metal halide are used instead of high-or low-pressure sodium lamps, a lower average illuminance can be used. A series of tests were carried out under mesopic conditions to validate the trade-off and this article reports on the new visual performance results. Four tests were carried out: acuity of achromatic and chromatic targets, achromatic contrast detection threshold and colour identification, these being for on-axis targets. It was found that SPD did not affect the performance of achromatic tasks except for an increase in contrast detection threshold under LPS lamps. The performance of an acuity task using coloured targets displayed interaction between target colour and SPD.Colour naming accuracy was found to be significantly higher for metal halide lamps than for sodium lamps. For all tasks there was a reduction in visual performance at lower illuminances, and therefore a reduction in design illuminance leads to a reduction in the performance of some visual tasks which may not be offset by lamp SPD. Implications for the performance of real pedestrian tasks are discussed. 2 IntroductionIn the UK, where lighting in subsidiary streets is designed for the demands of the pedestrian, the design illuminance is specified through two documents. BS EN 13201-2:2003 1 describes the minimum maintained average horizontal photopic illuminance for six lighting classes, the Sseries, ranging from S6 = 2.0 lx to S1 = 15.0 lx, with intermediate levels being Pedestrians are faced with many different visual performance tasks, ranging from the essential, such as recognising the key features of the environment and detecting the raised edge of a paving slab, to the highly desirable, such as first detecting someone approaching and then seeing the details of the face of whoever is approaching 5. Most such tasks first require off-axis detection followed by the use of the fovea to see detail, which can be characterised by measures of visual acuity and contrast sensitivity, and the ability to discriminate colours, which can be characterised by measures such as the accuracy of colour naming. If the trade-off between illuminance and CRI is adopted, then MH lighting at the lower illuminance needs to produce the same, or better, 3 visual acuity, contrast sensitivity, colour naming ability and off-axis detection than HPS lighting at the higher illuminance if it is to be considered as providing acceptable lighting for pedestrians.Fotios, Cheal & Boyce 3 reviewed previous studies of visual performance carried out under mesopic conditions. Two recent studies 6,7 suggested that SPD does not affect achromatic, foveal acuity. One of these 6 used a single fluorescent lamp with a series of filters to vary SPD rather than compare actual lamps used for street lighting. Two earlier studies 8,9 had hinted that SPD may affect acuity although they offer insufficient inform...

Road lighting research for drivers and pedestrians: The basis of luminance and illuminance recommendations

“…For foveal acuity, the data suggest that higher luminance may enhance acuity but do not suggest that changes in SPD have significant effect. 91–93 SPD is expected to have an effect on visual performance, in mesopic conditions, for targets that stimulate regions of the retina beyond the fovea, either by size or by off-axis location. This can be seen in the study by Lewis 94 who measured threshold luminance contrast of back-illuminated transparencies of sinusoidal contrast gratings, which subtended a visual field of approximately 13° wide and 10° high.…”

A review of design recommendations for P-class road lighting in European and CIE documents – Part 1: Parameters for choosing a lighting class

“…a pedestrian) subtends a smaller visual size. While higher luminance increases visual acuity, 16 the ability to see small details, at a certain point the change in acuity with further increase of luminance becomes negligible. 17,18 It is therefore expected that a higher light level may enhance safety when driving at faster speed by increasing the ability to detect and identify likely hazards.…”

Investigating the chromatic contribution to recognition of facial expression

“…There is evidence 7 that lighting of higher short-wavelength content improves spatial brightness which is associated with judgements of reassurance 23 and aids the detection of trip hazards in peripheral vision. 8,50,51 Lighting of better colour rendering leads to a more preferred environment 14 and to better ability to identify colours [52][53][54] which may in turn assist with tasks such as witness descriptions of criminal acts. What this means is that if illuminance were to be decreased, this reduction might be offset by changes to lamp SPD for some tasks, but it would not be offset for recognition of facial expression.…”