Claudia M. Hunter

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.

The impact of spectral power distribution on the performance of an achromatic visual task

This experiment tests the hypothesis that light sources that produce smaller pupil sizes ensure better achromatic visual task performance at the same photopic illuminance. Two groups of subjects, one in the age range 18-28 years and the other in the range 61-78 years, performed a Landolt ring task for eight different gap sizes, two different illuminances, and two lamp scotopic/photopic ratios. For both age groups, pupil size was determined by both illuminance and lamp spectrum. The speed and accuracy of performance of the task was determined by the gap size, and to a much lesser extent, by the illuminance. Lamp spectrum had no effect on the performance of the task.

RESPONSE TO SIMULATED TRAFFIC SIGNALS USING LIGHT-EMITTING DIODE AND INCANDESCENT SOURCES

Simulated light-emitting diode (LED) traffic signals of different luminances were evaluated relative to incandescent signals of the same nominal color and at the luminances required by the specifications of the Institute of Transportation Engineers. Measurements were made of the reaction times to onset and the number of missed signals for red, yellow, and green incandescent and LED signals. Measurements also were made of subjects’ ability to correctly identify signal colors and of their subjective brightness and conspicuity ratings. All measurements were made under simulated daytime conditions. There were no significant differences in mean reaction time, percentage of missed signals, color identification, or subjective brightness and conspicuity ratings between simulated incandescent and LED signals of the same nominal color and luminance. Higher luminances were needed for the yellow and green signal colors to ensure that they produced the same reaction time, the same percentage of missed signals, and the same rated brightness and conspicuity as a red signal at a given luminance. Equations fitted to the reaction time data, the missed signals data, and the brightness and conspicuity ratings for the LED signals can be used to make quantitative predictions of the consequences of proposed changes in signal luminance for reaction time, brightness, and conspicuity.

EVALUATION OF HIGH INTENSITY DISCHARGE AUTOMOTIVE FORWARD LIGHTING

An experimental field investigation is described that compares the off-axis visual performance of HID forward lighting systems with comparable halogen systems to determine the relative visual effects of HID lighting. This has been accomplished for European beam patterns; North American beam patterns are currently being examined. The goal of the investigation is to determine if the higher off-axis intensity levels combined with the spectral properties of HID lamps provide any benefits to visual performance over conventional tungsten halogen lamps. In this study three current production European headlamp systems, one HID and two halogen, are compared. These systems are used to illuminate a fixed scene. Subjects perform a visual tracking task, cognitively similar to driving, while, simultaneously, small targets located at various angles in the periphery are activated. Subjects release a switch upon detection and reaction times and missed signals are measured. From the results, comparisons are made among the HID and halogen systems in terms of reaction time to signals at different peripheral angles, and in terms of numbers of missed signals. The results are compared to a model that predicts visibility at nighttime (mesopic) light levels. Potential implications of the results on driving safety and on the development or refinement of forward lighting standards are discussed.

The impact of daytime light exposures on sleep and mood in office workers

Background: By affecting the internal timing mechanisms of the brain, light regulates human physiology and behavior, perhaps most notably the sleep–wake cycle. Humans spend over 90% of their waking hours indoors, yet light in the built environment is not designed to affect circadian rhythms. Objective: Using a device calibrated to measure light that is effective for the circadian system (circadian‐effective light), collect personal light exposures in office workers and relate them to their sleep and mood. Setting: The research was conducted in 5 buildings managed by the US General Services Administration. Participants: This study recruited 109 participants (69 females), of whom 81 (54 females) participated in both winter and summer. Measurements: Self‐reported measures of mood and sleep, and objective measures of circadian‐effective light and activity rhythms were collected for 7 consecutive days. Results: Compared to office workers receiving low levels of circadian‐effective light in the morning, receiving high levels in the morning is associated with reduced sleep onset latency (especially in winter), increased phasor magnitudes (a measure of circadian entrainment), and increased sleep quality. High levels of circadian‐effective light during the entire day are also associated with increased phasor magnitudes, reduced depression, and increased sleep quality. Conclusions: The present study is the first to measure personal light exposures in office workers using a calibrated device that measures circadian‐effective light and relate those light measures to mood, stress, and sleep. The studys results underscore the importance of daytime light exposures for sleep health.

Traffic Signal Luminance and Visual Discomfort at Night

The visual discomfort from simulated traffic signals under nighttime viewing conditions was assessed. Discomfort increased with increasing signal luminance and decreasing viewing distance. Color identification of signals was very high for all signal colors and luminances studied. Red signals meeting luminous intensity specifications of ITE and specifications being drafted in Europe were unlikely to cause visual discomfort under the conditions tested. Green and yellow signals meeting ITE and European specifications were more likely to cause visual discomfort. Dimming signals using light-emitting diodes might be a feasible strategy for minimizing discomfort under some nighttime viewing conditions.

Mapping the physical world to psychological reality: creating synthetic environments

The successful creation of telepresence and virtual environments requires a change in design paradigm. We must move away from attempts to recreate reality in its entirety toward the creation of environments that are psychologically real for humans, because in fact, reality mediated through display devices is largely subjective. The experiments discussed in this paper show that a single intrinsic physical property, such as the velocity or stability of a vehicle, can give rise to a multitude of subjective perceptions-for example, that the vehicle is moving faster than it really is, or that it is more likely to tip over going into a turn. These perceptions can easily be manipulated through knowledge of the variables and relationships involved, such as the effect of camera height. Designers can use this knowledge to create systems that promote desirable behaviors and limit dangerous or unproductive behaviors.

Measuring Light at Night and Melatonin Levels in Shift Workers: A Review of the Literature:

Shift work, especially that involving rotating and night shifts, is associated with an increased risk of diseases, including cancer. Attempts to explain the association between shift work and cancer in particular have focused on the processes of melatonin production and suppression. One hypothesis postulates that exposure to light at night (LAN) suppresses melatonin, whose production is known to slow the development of cancerous cells, while another proposes that circadian disruption associated with shift work, and not just LAN, increases health risks. This review focuses on six studies that employed quantitative measurement of LAN and melatonin levels to assess cancer risks in shift workers. These studies were identified via searching the PubMed database for peer-reviewed, English-language articles examining the links between shift work, LAN, and disease using the terms light at night, circadian disruption, health, risk, cancer, shift work, or rotating shift. While the results indicate a growing consensus on the relationship between disease risks (particularly cancer) and circadian disruption associated with shift work, the establishment of a direct link between LAN and disease has been impeded by contradictory studies and a lack of consistent, quantitative methods for measuring LAN in the research to date. Better protocols for assessing personal LAN exposure are required, particularly those employing calibrated devices that measure and sample exposure to workplace light conditions, to accurately assess LAN’s effects on the circadian system and disease. Other methodologies, such as measuring circadian disruption and melatonin levels in the field, may also help to resolve discrepancies in the findings.

Visual Benefits of High-Intensity Discharge Automotive Forward Lighting

This paper describes a study that compares the relative merits of high-intensity discharge vehicle headlamps with conventional halogen vehicle headlamps. Reaction times of study participants are measured. The study has implications for driving safety and for the ways in which it would be useful to refine vehicle headlamps.