Jennifer A. Brons

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.

Measurements of light at night (LAN) for a sample of female school teachers

Epidemiological studies have shown an association between rotating shiftwork and breast cancer (BC) risk. Recently, light at night (LAN) measured by satellite photometry and by self-reports of bedroom brightness has been shown to be associated with BC risk, irrespective of shiftwork history. Importance has been placed on these associations because retinal light exposures at night can suppress the hormone melatonin and/or disrupt circadian entrainment to the local 24-h light-dark cycle. The present study examined whether it was valid to use satellite photometry and self-reports of brightness to characterize light, as it might stimulate the circadian system and thereby affect BC incidence. Calibrated photometric measurements were made at the bedroom windows and in the bedrooms of a sample of female school teachers, who worked regular dayshifts and lived in a variety of satellite-measured sky brightness categories. The light levels at both locations were usually very low and were independent of the amount of satellite-measured light. Calibrated photometric measurements were also obtained at the corneas of these female school teachers together with calibrated accelerometer measurements for seven consecutive days and evenings. Based upon these personal light exposure and activity measurements, the female teachers who participated in this study did not have disrupted light-dark cycles like those associated with rotating shiftworkers who do exhibit a higher risk for BC. Rather, this sample of female school teachers had 24-h light-dark and activity-rest patterns very much like those experienced by dayshift nurses examined in an earlier study who are not at an elevated risk of BC. No relationship was found between the amount of satellite-measured light levels and the 24-h light-dark patterns these women experienced. It was concluded from the present study that satellite photometry is unrelated to personal light exposures as they might affect melatonin suppression and/or circadian disruption. More generally, photometric devices calibrated in terms of the operational characteristics of the human circadian system must be used to meaningfully link LAN and BC incidence. (Authors correspondence: E-mail: ream@rpi.edu)

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.

Parking lot lighting based upon predictions of scene brightness and personal safety

Providing subjective impressions of security is central to outdoor lighting design. Current parking lot lighting recommendations are based upon photopic illuminances, regardless of spectrum. Scene brightness perception is directly related to impressions of security, and depends upon both light level and spectrum. A provisional model was used to predict scene brightness for three parking lots, each illuminated to different levels by different light sources. Observers judged scene brightness, security and other factors for each lot. The provisional model accurately predicted both scene brightness and security judgements. The lighting associated with the best subjective ratings also had the lowest power density. A design method using ‘brightness illuminance’ is presented, which can lower system costs while maintaining a sense of security by users.

Spectral considerations for outdoor lighting: Designing for perceived scene brightness

Photopic illuminance is the photometric metric used today for specifying parking lot lighting levels. The photopic luminous efficiency function does not represent the spectral sensitivity of the perceived scene brightness of parking lots. Sources with a greater proportion of short-wavelength radiation will be seen as brighter for the same photopic illuminance. Moreover, the psychological benefit of providing people with a sense of safety and security in a parking lot is better correlated with the perceived brightness of the parking lot than with its photopic illuminance. Because photopic illuminance is not predictive of the psychological benefit expected from the parking lot lighting system, electric energy will be unnecessarily wasted if specifications are based upon this metric. Specifying parking lot lighting with a benefit metric based upon perceived scene brightness could reduce electric power requirements as well as the amount of radiant energy reflecting from the pavement and escaping into the night sky. A method of equating brightness for different spectral power distributions is provided.