Leora C Radetsky

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.

Conceptual design metrics for daylighting

Daylight is a key component of green building; however, no prevailing metric has emerged to help identify buildings that are well-daylit buildings. This paper proposes a ‘daylighting dashboard’; a visual representation of a design’s potential to meet eight design goals: average illuminance, coverage, diffuse daylight, daylight autonomy, circadian stimulus, glazing area, view and solar heat gain. This metric allows for informed decisions to be made early in the conceptual phase of design, and highlights aspects of design that may need further development, while there is still the opportunity to make modifications. These eight goals should be prioritized as appropriate for individual projects, rating systems or code requirements. This early indication of performance of conceptual design alternatives is likely to guide architects to better daylit buildings.

Influence of Spectral Power Distribution on Scene Brightness at Different Light Levels

ABSTRACT Exterior lighting has multiple objectives. Brightness perception is a relevant parameter for outdoor lighting because it is correlated with perceptions of safety and security. Understanding the influence of the spectral characteristics of lighting to scene brightness perception is important in order to devise exterior lighting specifications that support perceptions of safety and security in exterior lighted environments, as well as to optimize light source technologies to account for these factors. A study of scene brightness perception under different light levels and spectral power distributions was conducted to assess whether scene brightness perception exhibited increased short-wavelength spectral sensitivity as a function of increasing light level. The results confirm that a successful model of spectral sensitivity for scene brightness perception should incorporate a shift in short-wavelength sensitivity like the one investigated in the present study.

Testing a provisional model of scene brightness with and without objects of different colours

A provisional model of brightness perception for illuminated outdoor scenes was recently proposed based upon a combination of photopic and short-wavelength cone spectral sensitivities, where short-wavelength cone sensitivity increases with radiance. An experiment was undertaken to determine whether coloured objects within the illuminated scenes affected overall scene brightness perception and, in so doing, to provide a test of the provisional model. The results suggest that overall scene brightness perceptions are, for the range of light sources and light levels selected, consistent with the provisional model and that scene brightness perception is independent of object colours within the illuminated scenes.

Circadian Disruption: comparing humans with mice

Disruption of the 24-h light-dark cycle has been implicated as an endocrine disruptor and linked to increased morbidity and mortality in animal studies. Previously reported measurements of circadian disruption in day-shift and rotating-shift nurses were compared with new mouse data where the light-dark patterns simulated shiftwork. Phasor magnitudes, a measure of circadian entrainment, were shown to be similar for humans and for mice when exposed to similar patterns of light and dark. Phasor analyses may be a useful method for quantitatively bridging ecological measurements of circadian disruption in human with parametric studies of health outcomes in a mouse model.

Glucose tolerance in mice exposed to light–dark stimulus patterns mirroring dayshift and rotating shift schedules

Glucose tolerance was measured in (nocturnal) mice exposed to light–dark stimulus patterns simulating those that (diurnal) humans would experience while working dayshift (DSS) and 2 rotating night shift patterns (1 rotating night shift per week [RSS1] and 3 rotating night shifts per week [RSS3]). Oral glucose tolerance tests were administered at the same time and light phase during the third week of each experimental session. In contrast to the RSS1 and RSS3 conditions, glucose levels reduced more quickly for the DSS condition. Glucose area-under-the-curve measured for the DSS condition was also significantly less than that for the RSS1 and RSS3 conditions. Circadian disruption for the 3 light–dark patterns was quantified using phasor magnitude based on the 24-h light–dark patterns and their associated activity–rest patterns. Circadian disruption for mice in the DSS condition was significantly less than that for the RSS1 and RSS3 conditions. This study extends previous studies showing that even 1 night of shift work decreases glucose tolerance and that circadian disruption is linked to glucose tolerance in mice.

Spectral sensitivity and scene brightness at low to moderate photopic light levels

A study of scene brightness perception was conducted to assess whether spectral sensitivity for scene brightness perception at low to moderate light levels (∼3–110 lux) could be partially explained by a contribution of intrinsically photosensitive retinal ganglion cells (ipRGC). An experiment was conducted at two different light level ranges and using two different spectral power distributions. The results suggest an increase in short-wavelength spectral sensitivity as a function of increasing light level. The results also confirm that including ipRGC as well as cone photoreceptor input in scene brightness spectral sensitivity resulted in improved predictions compared to including either cone input only or rod as well as cone input.

Toward the development of standards for yellow flashing lights used in work zones

Flashing yellow warning lights are important for worker and driver safety in work zones. Current standards for these lights do not address whether and how they should be coordinated to provide directional information to drivers navigating through work zones. A field study was conducted to assess driver responses to warning lights. The luminous intensities and flash patterns of warning lights along a simulated work zone were varied during daytime and nighttime. During the daytime, driver responses were relatively insensitive to warning light characteristics, although drivers preferred sequential and synchronised flash patterns over random, uncoordinated flashing. At nighttime, the combination of a temporal peak luminous intensity of 25 cd and a sequential flash pattern was optimal for providing directional information. A single initial warning light having a higher luminous intensity may help drivers detect the work zone without creating unacceptable visual discomfort.

The Value of Red Light at Night for Increasing Basil Yield

Abstract: Sweet basil (Ocimum basilicum L.) is primarily used for culinary purposes, but it is also used in the fragrance and medicinal industries. In the last few years, global sweet basil production has been significantly impacted by downy mildew caused by Peronospora belbahrii Thines. Nighttime exposure to red light has been shown to inhibit sporulation of P. belbahrii. The objective of this study was to determine if nighttime exposure to red light from light-emitting diodes (λmax = 625 nm) could increase plant growth (plant height and leaf size) and yield (number and weight of leaves) in basil plants. In two sets of greenhouse experiments, red light was applied at a photosynthetic photon flux density of 60 μmol m-2 s-1 during the otherwise dark night for 10 h (from 2000 to 0600). The results demonstrate that exposure to red light at night can increase the number of basil leaves per plant, plant height, leaf size (length and width), and leaf fresh and dry weight compared with plants in darkness at night. The addition of incremental red light at night has the potential to be cost-effective for fresh organic basil production in controlled environments.