Peter Boyce

Lighting appraisal, well-being and performance in open-plan offices: A linked mechanisms approach:

In two experiments in a simulated office space, temporary office personnel worked under one of six lighting conditions for a day. A previous paper reported the results of statistical tests for lighting conditions effects on perceptions, feelings and task performance. This paper reports mediated regression analyses testing the linked mechanisms by which lighting conditions affect health, well-being and task performance. Combined results from the two statistical approaches show that people who perceived their office lighting as being of higher quality rated the space as more attractive, reported more pleasant mood, and showed greater well-being at the end of the day. Direct—indirect lighting and personal control were favoured. Lighting conditions that improved visibility also improved task performance.

Occupant use of switching and dimming controls in offices

As part of a larger study sponsored by the Light Right Consortium, temporary office workers spent a day in an office working under one of four different lighting installations. For two of these installations the office workers had the freedom to adjust the lighting of the cubicles they occupied: either with a switchable desk lamp, or varying the direct component of a continuously dimmable overhead direct/indirect luminaire. This paper examines the illuminances chosen under these two conditions, compares the results with those found in other field and laboratory studies, and addresses pertinent questions about the behaviour of office workers when they have the freedom to adjust the lighting of their workspaces.

Lighting quality and office work: two field simulation experiments

This paper describes two experiments concerning the effects of variations in lighting quality on office worker performance, health, and well-being. Experiment 1 had four experimental conditions: a regular array of fully direct recessed parabolic luminaires; direct/indirect luminaires with no control; direct/indirect luminaires with a switchable desk lamp; and, workstation-specific direct/indirect luminaires with control over the direct portion. Experiment 2 contrasted two conditions with no individual lighting control: a regular array of recessed prismatic lensed luminaires, and suspended direct/indirect luminaires. Participants considered the direct/indirect systems to be more comfortable than the direct-only systems, with a further increase in comfort associated with individual control in Experiment 1. There were no simple main effects of lighting quality on the performance of any task, although the expected changes in performance associated with task visibility, practice, and fatigue were found. Interactions between lighting quality and time suggested that having a degree of individual control of lighting tended to maintain motivation and vigilance over the day.

Investigations of the subjective balance between illuminance and lamp colour properties

The paper reports two experiments concerned with the balance between illuminance and lamp colour properties for equal satisfaction with visual appearance. The first demonstrates the existence of this balance over a wide range of interior colourfulnesses. An explanation, based on the influence of lamp type and illuminance on the saturation of colours in an interior is proposed, which suggests that Colour Discrimination Index should be a better predictor of the magnitude of the balance than Colour Rendering Index. To test this suggestion the second experiment was designed, using both coloured and achromatic interiors. The results for the coloured interior support the earlier study and lead to the conclusion that Colour Discrimination Index is a better predictor. The results for the achromatic interior are of a different nature.

Effect of correlated colour temperature on the perception of interiors and colour discrimination performance

A feature of many national lighting standards is the recommendation that lamps with high correlated colour temperatures should not be used at low illuminances. The technical justification for this advice is limited so two experiments have been conducted to explore its validity. In the first experiment, fifteen observers carried out colour discrimination tasks and assessed the lighting of a small room lit to different illuminances using lamps with good colour rendering properties but with different correlated colour temperatures. The room decor was achromatic but natural colour, in the form of fruit and flowers, was introduced as another variable. In the second experiment, ten observers carried out colour discrimination tasks and made assessments of the lighting of the same room lit to 225 lx, but decorated with blue or pink walls and lit by lamps with good colour rendering properties but different correlated colour temperatures. Again, natural colour, in the form of fruit and flowers, was introduced as another variable. Analyses of the assessments of the lighting of the room showed that one major factor determining the impression given by the lighting was the illuminance. Increasing the illuminance made the lighting of the room appear more pleasant, more comfortable, clearer, more stimulating, brighter, more colourful, more natural, more friendly, more warm, more uniform, less hazy, less oppressive, less dim and less hostile. The correlated colour temperature of the lamps used had virtually no effect on the observers impression of the lighting of the room. The other major factor influencing the impression of the lighting of the room was the presence of natural colour. Introducing natural colour, in the form of fruit and flowers, enhances the positive impressions created by the lighting, particularly at the higher illuminances. This enhancement occurs regardless of the correlated colour temperature of the lamps being used. It can be concluded that the advice limiting the use of high correlated colour temperature lamps in rooms lit to low illuminances is unnnecesarily restrictive. The results obtained suggest that provided the occupants are fully adapted to the lighting the correlated colour temperature of the lamp has little effect on peoples impressions of the lighting of the room.

Review: The Impact of Light in Buildings on Human Health:

The effects of light on health can be divided into three sections. The first is that of light as radiation. Exposure to the ultraviolet, visible, and infrared radiation produced by light sources can damage both the eye and skin, through both thermal and photochemical mechanisms. Such damage is rare for indoor lighting installations designed for vision but can occur in some situations. The second is light operating through the visual system. Lighting enables us to see but lighting conditions that cause visual discomfort are likely to lead to eyestrain. Anyone who frequently experiences eyestrain is not enjoying the best of health. The lighting conditions that cause visual discomfort in buildings are well known and easily avoided. The third is light operating through the circadian system. This is known to influence sleep patterns and believed to be linked to the development of breast cancer among night shift workers. There is still much to learn about the impact of light on human health but what is known is enough to ensure that the topic requires the attention of all those concerned with the lighting of buildings.

Lighting the graveyard shift: The influence of a daylight-simulating skylight on the task performance and mood of night-shift workerst

This experiment was designed to establish whether lighting provided by a daylight-simulating skylight could be used to enhance the task performance and mood of night-shift workers. Subjects performed a series of cognitive tasks, gave subjective ratings of their mood and had their core temperature measured six times during each shift, for three successive nights, under the same lighting condition. Each shift ran from 00.00 hours to 07.59 hours. The subjects also kept a daily diary recording their general health, times of sleep and sleep quality for the complete period of the experiment. Four lighting conditions were experienced: a fixed low-illuminance condition; a fixed high-illuminance condition; an increasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from dawn to midday; and a decreasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from midday to dusk. There was a three day rest period before exposure to each lighting condition. The high, increasing and decreasing illuminance conditions produced higher core body temperatures and greater subjective arousal than did the low illuminance condition, on all three nights. The high- and decreasing-illuminance conditions improved the performance of complex cognitive tasks relative to the low and increasing illuminance conditions, on all three nights. There was no difference between the lighting conditions for the performance of simple cognitive tasks. The high illuminance condition led to a greater delay in going to bed following the shift than did the low-illuminance condition.

Age, illuminance, visual performance and preference:

Relationships between age, illuminance, visual performance and preference are derived from tests in which 150 subjects performed four tasks: self- and externally-paced Landolt-ring charts, conveyor inspection and a tracker task. Replies to questionnaires enabled preferences to be estimated. Performance results indicate a strong interaction between age and illuminance for the Landolt-ring tasks but not for the conveyor or tracker task. Differences in performance of the Landolt-ring task are largely eliminated by an increase in illuminance. The preference results indicate a decrease in task difficulty and an increase in satisfaction as the illuminance is increased.

Hue discrimination and light sources

Eight experiments are briefly described in which the influence of lamp type, illuminance and subjects age and experience on the performance of the Farnsworth-Munsell 100 hue test were examined. Statistical analysis showed that either the CIE gamut area or the colour rendering index of the lamp type could be used as an approximate predictor of the level of performance on the test; the larger the CIE gamut area or the higher the colour rendering index, the better the performance. Compared with the effect of lamp type the influence of illuminance was small, the only significant effect being an improvement in performance at higher illuminances for the older age group. Age itself had a large effect. The older age group consistently produced much worse performances than the young or middle age groups. Experience was not found to be a significant factor.

Lighting for Driving : Roads, Vehicles, Signs, and Signals

This book conveys the crucial role lighting plays in road safety and examines how it might be used more effectively, explains the thinking and scientific reasoning behind various forms of lighting, and analyzes the contribution of street lighting to the drivers understanding of real and potential road hazards. Filled with useful information, this resource straightforwardly addresses a wide range of safety factors encountered in actual driving situations, such as glare, inclement weather, complex signage, and driver age. It also deals with the often-ignored consequences of too much light, such as light trespass and sky glow. Organizing lighting requirements from the perspective of driving tasks rather than technology this book: details the effects of light spectrum; incorporates a coherent philosophy for lighting based on the supply of visual information; provides a review of the latest findings on the most effective use of lighting for road safety; and examines future trends in road, signal, and vehicle lighting.