nan Rea

A proposed unified system of photometry

,!A unified system of photometry is proposed that is based on human vision and allows the specification of visual stimuli at all light levels. To be useful, however, photometry can never be entirely synonymous with vision. Additivity is an essential characteristic of photometry, yet many visual responses, such as brightness matching, incorporate visual channels that are inherently non-additive in responding to light. Following a review of models of mesopic photometry based on a number of experimental techniques, a system of photometry based on reaction times is proposed to bridge conventional photopic and scotopic luminous efficiency functions through the mesopic region. The basis for the unified system is a parameter, X, which describes the proportion of photopic luminous efficacy at any luminance, and luminance can be calculated from a simple closed-form equation. The utility of the system is described, including instrumentation for the measurement of unified luminance.

Circadian photobiology: an emerging framework for lighting practice and research

A century of research and practice have optimized the use of electric lighting in buildings to support human vision. However, recent lines of research show that light is also important to human circadian regulation, as reflected in such diverse phenomena as depression, sleep quality, alertness, and, perhaps, even health. Although light is essential to both vision and circadian regulation, research shows that the biophysical processes that govern circadian regulation are very different from those that govern vision. This growing body of research will probably influence the architectural lighting community and manufacturers to reoptimize the use of electric lighting in buildings to support both human vision and circadian functions. The present paper is concerned with establishing a framework for lighting practice and applied research that will assist lighting practitioners and manufacturers in interpreting this emerging research.

Modelling the spectral sensitivity of the human circadian system

It is now well established that the spectral, spatial, temporal and absolute sensitivities of the human circadian system are very different from those of the human visual system. Although qualitative comparisons between the human circadian and visual systems can be made, there still remains some uncertainty in quantitatively predicting exactly how the circadian system will respond to different light exposures reaching the retina. This paper discusses attempts to model the spectral sensitivity of the circadian system. Each of the models discussed here varies in terms of its complexity and its consideration of retinal neuroanatomy and neurophysiology. Future testing to validate or improve any of these computational models will require a targeted hypothesis, as well as a suitably high level of experimental control before one model can be rejected in favour of another. Until specific hypotheses are formulated and tested, it would be premature to recommend international acceptance of any model or system of circadian photometry.

Several Views of Metal Halide and High-Pressure Sodium Lighting for Outdoor Applications

Metal halide (MH) lighting systems are gaining in acceptance relative to high-pressure sodium (HPS) lighting systems for many night time applications. The present paper describes a series of studies carried out to address some of the ‘quality’ issues associated with MH and HPS lighting systems. HPS and MH installations were compared in terms of perceptions of brightness and safety, acceptability for social interaction, facial recognition and eyewitness identification. At equal photopic light levels, a street scene illuminated at night by an MH lighting system was reliably seen as brighter and safer than the same scene illuminated by an HPS system. In terms of acceptability for social interaction, facial recognition and many aspects of eyewitness identification, the measured differences between lighting systems were not as clear.

Toward a model of outdoor lighting scene brightness

Light quantities based on the photopic luminous efficiency function do not predict brightness perceptions of lighted outdoor scenes such as streets, parking lots and plazas. This paper summarises a series of experiments conducted using scale-model outdoor scenes illuminated by different light sources to assess judgements of brightness. From the results and from previously published literature on the relative increase in short-wavelength spectral sensitivity for brightness, a tentative model for brightness perception of outdoor scenes is proposed. The model can serve as a starting point for efficiently testing future hypotheses regarding brightness perception in lighted outdoor scenes.

Outdoor site-lighting performance: A comprehensive and quantitative framework for assessing light pollution

Outdoor Site-Lighting Performance (OSP) is a comprehensive method for predicting and measuring three different aspects of light pollution: glow, trespass and glare. OSP is based upon the philosophy that a rational framework is necessary for optimising private and public desires for and against night-time lighting. Results are presented from over one hundred outdoor lighting installations that provide an empirical foundation for acknowledging the benefits of night-time lighting while establishing limits on light pollution. Recommended limits for glow, trespass and glare are offered to stimulate discussion among all stakeholders concerned with night-time lighting.

Predicting discomfort glare from outdoor lighting installations

In addition to sky glow and light trespass, discomfort glare from outdoor lighting installations is a growing concern to the public. A series of experimental investigations was performed to assess the relative impacts of light source photometric characteristics on subjective ratings of discomfort glare. The results converge, demonstrating the influence of light source illuminance, surround illuminance and ambient illuminance on subjective judgements of discomfort glare. A simple model relating these photometric quantities is proposed for making predictions of discomfort glare from outdoor lighting installations. This model can be readily incorporated into existing frameworks for evaluating light pollution as well as into lighting calculation software.

Ecological measurements of light exposure, activity and circadian disruption

In humans, circadian rhythms have an average period of 24.2 hours. The 24-hour patterns of light and dark on the retina synchronise circadian rhythms to the local time on earth. Lack of synchronisation between the endogenous clock and the local time has been associated with a host of maladies. Therefore, it is important to measure circadian light exposures over the course of the 24-hour day and to be able to assess circadian entrainment and disruption in actual living environments. Presented is an overview of the recently developed Daysimeter, a personal measurement device for recording activity and circadian light exposure. When the Daysimeter is worn on the head, two light sensors near the eye are used to estimate circadian light exposures over extended periods of time. Phasor analysis combines the measured periodic activity-rest patterns with the measured periodic light—dark patterns to assess behavioural circadian entrainment/disruption. As shown, day-shift and rotating-shift nurses exhibit remarkably different levels of behavioural circadian entrainment/disruption. These new ecological measurement and analysis techniques may provide important insights into the relationship between circadian disruption and well-being.

The effects of red and blue light on alertness and mood at night

This study was designed to explore the roles that long- and short-wavelength lights have on momentary mood and alertness at night. Twenty-two subjects participated in a mixed-design experiment, where we measured the impact of two levels of long- and short-wavelength lights on brain activity and on self-assessments of alertness, sleepiness and mood. Measurements were obtained 60 minutes prior to, during and after light exposure. Results showed that the red and the blue lights increased electroencephalographic beta power (12—30 Hz), reduced sleepiness, and increased positive affect relative to the previous dim-light period indicating that alertness and mood can be affected by light without necessarily stimulating the melatonin pathway. The impact of light was modest, however, compared to the increase in fatigue over the course of the night.

Measuring circadian light and its impact on adolescents

A field study was conducted with eighth-grade students to determine the impact of morning light on circadian timing, sleep duration and performance. Before and during school hours for a week in February 2009, half the students studied wore orange glasses that minimised the short-wavelength light exposure needed for circadian system stimulation. A control group did not wear the orange glasses. The Daysimeter, a circadian light meter, measured light/dark exposures in both groups for 7 days. Circadian timing was significantly delayed for those students who wore orange glasses compared to the control group. Sleep durations were slightly, but not significantly, curtailed in the orange-glasses group. Performance scores on a brief, standardised psychomotor vigilance test and self-reports of well-being were not significantly different between the two groups.