Steve Fotios

Road lighting and energy saving

This paper examines how the lighting of roads in the UK might be changed so as to preserve the benefits while minimising energy consumption. It is divided into four sections, these being changes in technology, changes in patterns of use, changes in standards and contracts and changes in the basis of design. Useful changes in technology and patterns of use are available now, but their use will raise the question as to whether or not environmental considerations can override conventional financial constraints. Changes in standards and the basis of design are much more long term. Comparisons of road lighting standards used in different countries show significant differences that deserve examination. As for the basis of design, consideration of the importance of light to fatal and personal injury accidents of different types suggests that road lighting should be concentrated where pedestrians are common, not where speeds are highest. Ultimately, considering carefully what problem road lighting is intended to solve and whether or not road lighting is the best answer is the key to minimising the energy consumption of road lighting without diminishing road safety.

Lighting for subsidiary streets: investigation of lamps of different SPD.Part 2-Brightness

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.

Lamp colour properties and apparent brightness: a review

This paper reviews previous work exploring apparent brightness in interior spaces, in particular the relationship between lamp spectrum and illuminance. An understanding of this is beneficial to designers of interior lighting and to researchers investigating visual response to lighting. The review establishes reliable data from previous work, examines the correlation between descriptors of lamp colour properties and illuminance, and identifies some further work required.

Predicting lamp spectrum effects at mesopic levels. Part 1: Spatial brightness

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.

Investigating the use of an adjustment task to set the preferred illuminance in a workplace environment

An experiment was carried out to examine user preferences for light level using the method of adjustment. The study sought preferred illuminances under lighting from fluorescent lamps of different correlated colour temperature. It was hypothesised that the preferred illuminance would be influenced by variables inherent in the experimental design including the available stimulus range, the anchor (initial setting before adjustment) and adaptation time before onset of adjustment action. The experiment included three different stimulus ranges (21–482 lux, 38–906 lux and 72–1307 lux) and these lead to significantly different preferred illuminances (337 lux, 523 lux and 645 lux, respectively). The experimental results confirmed that stimulus range and anchor have significant effects on the outcome of the adjustment task, confirming the importance of considering and reporting these variables when determining user preference with this method.

Perception of electric light sources of different colour properties

An analysis of the experimental conditions by which V(λ) was determined suggests that it cannot account fully for the human response to light. Much experimental work has shown a discrepancy between luminance measurement and brightness perception. Experiments have been carried out to assess the visual perception of various fluorescent and sodium lamps. Two lamps are presented simultaneously in adjacent light booths. Observers are asked to balance the two for visual equality. Results have shown that a significant difference in illuminance is needed to match lamps of different spectral distribution for visual equality. Lamps of higher colour quality require lower illuminance than do lamps of poorer colour quality. The majority of observers expressed a preference to work in the booth illuminated by the source of higher colour quality, despite a significantly lower illuminance. The results are supported well by previous experiments on visual clarity.

Proposed UK guidance for lighting in residential roads

This paper reports a proposed new system for specifying illuminances and lamp types for equal visual effects at mesopic illuminances, developed within the mesopic lighting panel of the Institution of Lighting Professionals in the UK. This study is applied in residential streets and thus the visual tasks considered are those relevant for pedestrians. It is proposed that the benchmark lamp for residential streets in the UK is the low-pressure sodium lamp; if other types of lamps are used, and these have a CIE General Colour Rendering Index of Ra ≥ 60, then the average illuminance can be reduced by an amount that is determined using the new CIE system for mesopic photometry and is dependent on the scotopic/photopic ratio of the lamp.

Obstacle detection: A pilot study investigating the effects of lamp type, illuminance and age

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 (<45 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 (>60 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.

Light source spectrum, brightness perception and visual performance in pedestrian environments: a review

This review considers the impact of light source spectral power distribution (SPD) on brightness perception and visual performance in mesopic conditions, with emphasis on the comparison of metal halide (MH) and high pressure sodium (HPS) lamps. Models of mesopic vision predict that SPD is a significant variable in that at a HPS photopic luminance of 0.100 cd/m2, MH need only produce about 0.070-0.075 cd/m2 to be seen as equally bright. However, attempts to validate the predictions of these models in the field have met with mixed success. As for visual performance, experimentation has shown that there are effects of SPD in mesopic conditions, but the magnitude of these effects depends on the nature of the task. Three alternative approaches are suggested for comparing light sources with different SPDs in mesopic conditions.

Using eye-tracking to identify pedestrians’ critical visual tasks, Part 1. Dual task approach

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.