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55 Potential Environmental Impacts Current Guide The current AASHTO Roadway Lighting Design Guide (AASHTO 2018) includes a section on sky glow and light trespass. The chapter also discusses the BUG classification system as an additional means of classifying luminaires. Additional Considerations for LED Sources Environmental and health concerns have been raised regarding the use of LED sources and their spectral content. Research in human circadian rhythms has shown that exposure in the evening to blue light from LEDs in light sources and devices could disturb circadian rhythms and cause sleep loss by suppressing melatonin production (Cajochen et al. 2011; Chang et al. 2015; West et al. 2011). The shorter wavelengths from LEDs can also result in higher discomfort glare as compared with other light sources for the same photopic illuminance measured at the eye of the observer (Rea 2017). Another drawback of LED roadway lighting pertains to maintaining dark skies and limiting light trespass related to astronomical and ecological considerations. With the added blue content from the SPD of the LEDs, Rayleigh scattering of light in the atmosphere increases sky glow (Luginbuhl et al. 2009). LED light sources could also result in sky glow because they emit more energy in the shorter wavelengths. Shorter wavelengths scatter more than longer wavelengths, which can affect the visibility of stars from the earth (Kinzey et al. 2017). Sky glow is also affected by total light output from the light source and the distribution of light from the luminaire (uplight in particular) (Kinzey et al. 2017). In addition to the SPD, recent research shows that sky glow is also affected by aerosol content and the operating characteristics of the detector used to assess sky glow (Rea and Bierman 2014). Effects of sky glow can be mitigated with the use of adaptive lighting technology, which would minimize the total amount of flux generated from the source. Because of these concerns, a recent report by the American Medical Association, Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting H-135.927 (Kraus 2016), recommends the use of lower CCTs (possibly because of lower blue content in the SPD) to minimize potential ill effects on health and the environment. However, using CCT as a defining metric for determining harmful health effects from LED lighting is not accurate, because CCT is not the only factor involved in defining light exposure (Rea and Figueiro 2016). CCT is not a definitive metric for determining the blue content of a light source. Moreover, the spectral content of the LED light source determines the amount of blue light emitted. There is no metric for determining the blue content in an LED light source, other than measuring the energies of each wavelength that makes up the spectrum. The lack of an easy metric for determining the C H A P T E R 1 1
56 Solid-State Roadway Lighting Design blue content of LED light sources has led to the adoption of CCT by the lighting industry, but CCT is not a metric of the SPD; rather, CCT gives information on the color appearance of the light source. Dosage (the duration and intensity or level of light exposure) also plays an important role in disruption of circadian rhythms. A majority of the research on impact of light on circadian rhythms was conducted on shift workers or animals in controlled environments exposed to very high light levels (Borugian et al. 2005; CissÃ© et al. 2016, 2017; Dauchy et al. 2014; Fonken et al. 2013; Lewy et al. 1980; Schernhammer et al. 2003). However, the duration of exposure to street light is much shorter than the duration of light exposure experienced by shift workers. Light levels from street and outdoor lighting are also much lower than those in a lighted nighttime work environment (McLean and Lutkevich 2016). Furthermore, exposure to light levels from inside a personâs home could be much higher than exposure to light levels from street lighting (Kinzey 2016). This impact of lighting on a human is evident down to a certain threshold of illuminance level, below which lighting no longer affects the melatonin level (Figueiro et al. 2006). The dosage versus melatonin data from Figueiro and Kinzey are overlaid and shown in Figure 37, which shows that roadway levels are typically much lower than threshold and that other lighted objects within the household may have a greater impact than the roadway lighting. Another study that assessed the effect of melatonin suppression induced by indirect blue light from inside a stationary automobile reported that melatonin suppression did not occur when the subject was exposed to light levels of up to 1.25 lx (Lerchl et al. 2009). Some epidemiological studies that examined the effects of artificial light at night on the incidence of breast cancers found that higher levels of outdoor artificial light at night were correlated with a higher incidence of breast cancer (Hurley et al. 2014; Kloog et al. 2008, 2010; Portnov et al. 2016). For all these studies, outdoor nighttime light levels were estimated by using satellite imagery data from the U.S. Defense Meteorological Satellite Program, and light exposure was not measured at an individual level. Research also has showed that there is no relationship between light levels estimated from satellite imagery and light levels experienced by individuals (Rea et al. 2011). Source: Figueiro et al. (2006) and Kinzey (2016). Figure 37. Impact threshold of typical lighting levels on melatonin.
Potential Environmental Impacts 57 However, no existing research shows that either LED roadway lighting (of any SPD) at light trespass levels or exposure durations under realistic road conditions disrupts human circadian rhythms. Research shows that using LED roadway lighting results in longer detection distances. A human factors study that compared various types of LED and HPS sources in an urban roadway environment con- cluded that the CCT of an LED source could play an important role in detection distance and relative safety (Clanton and Associates Inc. 2014). Because CCT was the only metric available during testing, it was used as the metric of interest. This study incorporated a variety of colored targets on the roadway under matched LEDs with different CCTs dimmed to match the road surface luminance. The targets were in the roadway at points of equivalent vertical illuminance to control object contrast. In a foveal task, participants were asked to search for and indicate when they could perceive the target in the roadway. Because the targets were different colors, the benefit of the lighting was from color contrast. CCT was the only metric available during the period of this testing. The results of this research showed that objects lighted with a 4100K CCT had a detection distance as much as 20% higher than that of other color temperatures. The detection distances of color targets were also the highest for the 4100K CCT LED. Study results also indicated that, to achieve the same level of visibility with a 3000K light source, higher levels of light are required than with a 4000K light source. The higher light levels needed for the 3000K LEDs could increase power consumption by about 8% to 10% as compared with the 4000K LED (McLean and Lutkevich 2016). Therefore, reducing the blue spectral component in the light source may increase energy consumption. Researchers argue that, to correctly understand the effect of light on the disruption of circadian rhythms, the light stimulus must be measured in terms of circadian response rather than the conventional visual response (Figueiro 2017). One proposed mathematical model (Rea et al. 2005) allows the response of acute melatonin suppression to be predicted after 1 hour of expo- sure to a specific light level and light spectrum. The circadian light is comparable to photopic lux measured at the eye (but considers the circadian response of the eye) and can then be used to determine the circadian stimulus. The circadian stimulus is the effectiveness of the incident light in suppressing melatonin and ranges from 0 to 0.7, where 0.1 is the threshold circadian stimulus and 0.7 is the saturation circadian stimulus. Comparison of circadian light values for 4000K and 3000K LEDs showed that the 4000K LED was less effective at melatonin suppression than the 3000K LED (Rea 2017). The biological effects of light on humans can also be measured in terms of the response of the five potential photoreceptors in the eye (short-wavelength cones, medium-wavelength cones, long-wavelength cones, intrinsically photosensitive retinal ganglion cells, and rods), which can affect circadian responses (Lucas et al. 2014). The five sensitivity functions (one for reach receptor) can be used to calculate the activation of each of the receptors, which can help in comparing the light sources of different SPDs. Research that evaluated the effect of the duration of exposure and the light level from 3000K and 4000K LEDs on melatonin suppression shows that melatonin suppression was significantly affected by the duration of exposure and the light level (Lighting Research Center 2016). CCT (or the light source spectrum) did not significantly affect melatonin suppression. These results show that there are no discernable differences between the CCTs of 3000K and 4000K LEDs in terms of health effects; however, for the 3000K LED to maintain a level of visibility, as measured by detection distance, similar to that of the 4000K LED, a higher light level is required, which results in higher energy consumption. Research does not currently show health impacts from properly designed roadway lighting. The spectral content of LEDs can have an impact on light scatter, potentially on some species of wildlife, and has implications for the design of safety and detection distances. Impacts must be evaluated for the specific area for which lighting is being proposed.
58 Solid-State Roadway Lighting Design Other environmental impacts include the effect of roadway lighting significantly delaying the maturity of plants such as soybeans, which require a night cycle to mature. Research that evaluated the effect of HPS road lighting on the maturity of soybean plants in Illinois showed that soybeans exposed to light trespass were delayed from 2 to 7 weeks (Palmer et al. 2017). In a follow-up experiment, the impact of the LED light source on soybeans was slightly greater than that of the HPS. This field study aligned with the results of a study conducted in a lab that examined the effect of LEDs with increasing amounts of blue content on the growth and development of soybeans. The results of the lab study showed that plants grown under LEDs with higher blue content had shorter stems. Overall, the lab study showed that lighting with LEDs with lower blue content resulted in stem elongation and leaf expansion, whereas lighting with LEDs with higher blue content resulted in more compact plants. These results show that blue content on the spectrum of LED roadway lighting may influence the maturity of soybeans and that proper precautions must be taken to limit light trespass into fields adjacent to lighted roadways. Wildlife activities are also affected by the presence of artificial light. For example, the regular movements of hatchling marine turtles toward the sea occur primarily at night; the presence of artificial light disrupts their photic cues and can cause them to move away from the sea, which often leads to mortal consequences (Cope and Bugbee 2013). Specific breeds of bats (Peters and Verhoeven 1994) and mice (Rydell 1991) that forage predominantly in areas of darkness are affected adversely by artificial lighting. Because the health, growth, behavior, and maturity of some plants and wildlife can be affected by roadway lighting, it is important to engage in research that leads to favorable outcomes for both ecology and highway safety. Key Issues for Potential Environmental Impacts Much research has been done in the area of the health and environmental impacts of lighting at night, and much more research continues. Although impacts and considerations may further develop as more data are analyzed, the following key items are recommended for design. â¢ A well-designed roadway lighting system that uses the recommended light levels and meets the glare limits and light trespass values specified in the AASHTO Roadway Lighting Design Guide does not have any adverse health effects when typical 3000K or 4000K LED sources are used. â¢ Although LED sources are likely to cause greater light scatter and sky glow, these effects are often offset by reduced total lumens and limited light trespass. â¢ Impacts on wildlife and plants vary by species. Research for some species is limited. For system design, lighting should be at the lowest level recommended, light trespass should be limited, and sensitive species in the area of the lighting system should be studied. Mitigation, if any, should be documented if recommended (e.g., for turtle nesting grounds).