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56 Chapter 11 â Potential Environmental Impacts Current Guide The current AASHTO design guide 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 to blue light from LEDs in light sources and devices in the evening could disturb circadian rhythms and cause sleep loss by suppressing melatonin production(Cajochen, Frey, Spati, Bues, Pross, Mager, Wirz-Justice, & Stefani, 2011; Chang, Aeschbach, Duffy, & Czeisler, 2015; West, Jablonksi, B, Cecil, M, Ayers, Maida, Bowen, Sliney, Rollag, Hanifin, & Brainard, 2011). The shorter wavelengths from LEDs can also result in higher discomfort glare when compared to 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 added blue content from the SPD of the LEDs, Rayleigh scattering of light in the atmosphere increases sky glow(Luginbuhl, Duriscoe, Moore, Richman, Lockwood, & Davis, 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, Perrin, Miller, Kocifaj, Aube, & Lamphar, 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 & 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 the above-mentioned concerns, a recent report by the American Medical Association, Human and Environmental Effects of Light Emitting Diode Community Lighting, recommends the use of lower CCTs (possibly due to lower blue content in the SPD) to minimize potential ill effects on health and the environment(Kraus, 2016). However, using CCT as a defining metric for determining harmful health effects from LED lighting is not accurate because it is not the only factor involved in defining light exposure(Rea & Figueiro, 2016). CCT is not a definitive metric to determine 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 to determine the blue content in an LED light source other than measuring the energies of each wavelength that comprises the spectrum. The lack of an easy metric to determine the blue content of LED light sources has led to the adoption of CCT in 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(Borugain, RP, MC, TF, & KJ, 2005; Cisse, Peng, & Nelson, 2016, 2017; Dauchy, Xiang, Mao, Brimer, Wren, Yuan, Anbalagan, Hauch, Frasch, Rowan, Blask, & Hill, 2014; Fonken, Aubrecht, Melendez-Fernandez, Weil, & Nelson, 2013; Lewy, Wehr, FK, DA, & SP, 1980; Schernhammer, F, FE, WC, DJ, Kawachi, CS, & GA, 2003). For street lighting, however, the duration of exposure to light is much shorter than the
57 duration of exposure for shift workers. Light levels from street and outdoor lighting are also much lower than those in a lighted nighttime work environment(McLean, 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 the lighting on a human is evident down to a certain threshold of illuminance level, below which lighting no longer impacts the melatonin level (Figueiro, 2006). The dosage versus melatonin data from Figuerio and Kinzey are overlaid and shown in Figure 38, 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. Figure 38. Melatonin Impact Threshold of Typical Lighting Levels adapted from (Based on a model in Figueiro, 2006) and (Kinzey, 2016) Another study (Lerhl, Schindler, Eichhorn, F, & Erren, 2009) that assessed the effect of melatonin suppression induced by indirect blue light from inside a stationary automobile reported that there was no melatonin suppression when exposed to light levels of up to 1.25 lx. Some epidemiological studies that examined the effects of artificial light at night on incidence of breast cancers found that higher levels of outdoor artificial light at night were correlated with higher incidences of breast cancer(Hurley, Goldberg, Nelson, Hertz, PL, Bernstein, & Reynolds, 2014; Kloog, Haim, Stevens, Barchana, & Portnov, 2008; Kloog, Stevens, Haim, & Portnov, 2010; Portnov, Stevens, Samociuk, Wakefield, & Gregorio, 2016). For all these studies, outdoor nighttime light levels were estimated using satellite imagery data from the U.S. Defense Meteorological Satellite Program, and light exposure was not measured at an individual level. Research also showed that there is no relationship between light levels estimated from satellite imagery and light levels experienced by individuals(Rea, Research does not currently show health impacts from properly designed roadway lighting.
58 Brons, & Figueiro, 2011). However, no existing research shows that LED roadway lighting (of any SPD) at light trespass levels and exposure durations in realistic road conditions disrupts human circadian rhythms. Research shows that using LED roadway lighting results in longer detection distances. A human factors study (Clanton & Associates Inc., 2014) that compared various types of LED and HPS sources in an urban roadway environment concludes that the CCT of an LED source could play an important role in detection distance and relative safety. 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. As 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. Note that CCT was the only metric available during the time period of this testing. Results of this research found that objects lighted with a 4100K CCT had as much as a 20% higher detection distance over other color temperatures. 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% compared to the 4000K LED(McLean, 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, light stimulus must be measured in terms of circadian response rather than the conventional visual response(Figueiro, 2017). One proposed mathematical model (Rea, Figueiro, Bullough, & Bierman, 2005) allows the response of acute melatonin suppression to be predicted after one-hour exposure to a specific light level and light spectrum. The circadian light (CLA) is comparable to photopic lux measured at the eye (but considers the circadian response of the eye) and can then be used to determine circadian stimulus (CS). The CS is the effectiveness of the incident light at suppressing melatonin and ranges from 0 to 0.7, where 0.1 is the threshold CS and 0.7 is the saturation CS. Comparison of CLA 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 (short-wavelength cones, medium wavelength cones, long- wavelength cones, the intrinsically photosensitive retinal ganglion cells [ipRGCs], and rods) in the eye, which can affect circadian responses(Lucas, Peirson, Berson, Brown, Cooper, Czeizler, Figueiro, Gamlin, Lockley, O'Hagan, Price, Provencio, Skene, & Brainard, 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 time of exposure and light level from 3000K and 4000K LEDs on melatonin suppression (Lighting Research Center, 2016) shows that melatonin suppression was significantly affected by time of exposure and the light level. 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 the 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 the 4000K LED, a higher light level is required, which results in higher energy consumption. Other environmental impacts include the effect of roadway lighting significantly delaying the maturity of plants like soybeans that require a night cycle to mature. Research that evaluated the effect of HPS road lighting on the maturity of the soybean plants in Illinois showed that soybeans exposed to light trespass
59 were delayed from 2 to 7 weeks(Palmer, Gibbons, & Bhagavathula, 2017). In a follow-up experiment, the impact of the LED light source on soybeans showed a slightly higher impact than that of the HPS. This field study aligned with the results of a study conducted in a lab examined the effect of the LEDs with increasing amounts of blue content on the growth and development of soybeans and reported that higher blue content LEDs resulted in shorter stems(). Overall, lower blue content LEDs resulted in stem elongation and leaf expansion, and higher blue content LEDs 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 impacted by the presence of artificial light. For example, the regular movements of hatchling marine turtles toward the sea occur primarily at night but 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 & Bugbee, 2013). Specific breeds of bats(Peters & 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 plant 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 Much research has been done in the area of 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 using recommended light levels, meeting glare limits, and meeting light trespass values included in the AASHTO guide does not have any health effect using typical 3000K or 4000K LED sources. â¢ Although LED sources are likely to cause greater light scatter and sky glow, this is 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 and mitigation, if any, should be documented if recommended (e.g., for turtle nesting grounds). Spectral content of LEDs can have an impact on light scatter, potentially on some species of wildlife, and has implications for design of safety and detection distances. Impacts must be evaluated for the specific area lighting is being proposed.