This is something I wrote in high school. I think it's pretty cool. I also think that, given the age at which I wrote it, it's pretty good. You can see for yourself by reading it. Or just skim it. Whatever you'd like.
This is something I wrote in high school. I think it's pretty cool. I also think that, given the age at which I wrote it, it's pretty good. You can see for yourself by reading it. Or just skim it. Whatever you'd like.
What Color is Nighttime? An Analysis of Societal Priorities of Safety and Health in the Determination of the Appropriate Color Temperature of Streetlights
March 24, 2023
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Abstract
This paper presents the basic results of an inquiry into the factors involved when municipalities design their streetlighting systems. The historic purpose of the streetlight in Europe was for law enforcement. Anyone outside of their homes without carrying a light would be considered suspicious. The purpose of outdoor lighting evolved to become a government duty rather than an individual one. In the modern era, streetlights generally use HPS lighting technology, which emits a warm white light. With the onset of the LED, municipalities have been replacing their warm white HPS lights with cool white LEDs. The cool light provided by LEDs has the potential to increase road safety by keeping drivers awake and making objects more recognizable. However, the blue wavelengths involved in creating cool white light have the potential to damage people's eyes and impact people’s sleep. Ultimately, the subject of streetlighting can show something very important about the nature of municipal governments. The need to balance people’s wants and needs creates a near impossible problem for municipalities to solve, as it is difficult to create environments where both are properly addressed. Research conducted was done in the form of a literature review, and while original analysis is presented, no original research was conducted.
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Introduction
In January 2014, the City Council of Davis, California, voted to replace 2,600 streetlight fixtures utilizing High-Pressure Sodium (HPS) lighting technology with white LED fixtures. The city estimated that the switch would save them more than three and a half million dollars over the following 15 years (Greenwald, 2014). However, only 4 months into the installation process, complaints started rolling in from constituents. City residents complained about the new fixtures being too bright, producing too much glare, causing more light entry into their homes, increasing light pollution, and causing disturbances to their sleep (“Davis, CA LED Streetlight Retrofit”, 2019). One resident in particular sent a letter to the Mayor, claiming “I suspect you have just lowered residential property values by over $5,000 per home” (Greenwald, 2014). The residents' complaints all come back to the same issue, and it has nothing to do with the LED technology. Instead, it has to do with color temperature. The HPS lights that the city had been using for streetlighting had a color temperature of 2200K and the LED replacements had a color temperature of 4000K (“Davis, CA LED Streetlight Retrofit”, 2019).
Municipalities around the world have been swapping older, more energy demanding HPS fixtures in streetlights for new, more efficient LED sources (Stevens, 2016), and doing so presents a new variable to streetlighting. High-pressure sodium has been the most common form of outdoor lighting since its invention, due to its relative efficiency and long lifespan when compared to incandescent bulbs (Bullough et al., 2009). Light from HPS is monochromatic, meaning it only emits light at one wavelength, the equivalent of about 2100K. LEDs, on the other hand, can be made to emit light at almost any wavelength or equivalent temperature (European Commission [EC], n.d.). This fact has led to several different answers to the same question: What color temperature should streetlights be? Making that determination requires taking into account a number of complex and often conflicting issues that require the designation of priorities in health and safety. How people make that decision for their region has an immense impact on a smorgasbord of stakeholders.
Background
The darkness of night has evoked the imagination and fear of cultures for centuries. Wolfgang Schivelbusch, the author of Disenchanted Night: The Industrialization of Light in the Nineteenth Century, writes “The night is feminine, the day is masculine, and like everything feminine, it holds both repose and terror.” In the middle ages, the start of the night was marked in many European cities by the closing of the city gates. Houses were locked and keys given to local authorities for safekeeping. Curfews confined people to their homes and night watchmen patrolled the streets with torches, which were there not to light the way, but to make their carrier visible. Any individual venturing out past sunset for any reason also had to carry a torch for the same reason: to be seen. Otherwise, they would be seen as attempting to sneak past detection, and therefore were worthy of suspicion. An English decree from 1467 read “And no man walke after IX of the belle streken in the nyght withoute lyghte or withoute cause reasonable in payne of empresonment” (Schivelbusch, 1995, p. 82).
By the sixteenth century, the obligation to carry a torch had been extended to include putting a lantern outside the house. The Parliament of the City of Paris publicly declared that “during the months of November, December and January a lantern is to be hung out under the level of the first floor window sills before 6 o’clock every night. It is to be placed in such a prominent position that the street receives sufficient light.” This was the first form of public street illumination in Europe. The purpose was less to illuminate the street and more to illuminate the house for navigation and identification (Schivelbusch, 1995, 82).
The First Modern Streetlights
In the seventeenth century, municipalities began to take the task of nighttime illumination away from the people by placing government managed lanterns on poles by the street, which would be maintained by police (at this time, police were not simply law enforcement officials as they are today, but as maintainers of public works and enforcers of general, often authoritarian order). By providing light to the street, the government could extend its control of a city to all places that would otherwise be obscured by the dark (Schivelbusch, 1995, 84). This is the original purpose of streetlighting: to make the city safe at all times and to tame a time of lawlessness.
Definition of Color Temperature
Color temperature is a measurement of the spectral output of a light source. The higher the color temperature, the more short wavelength light it emits. The lower the color temperature, the more long wavelength light it emits. Humans perceive the color of light based on its wavelength, red being the longest visible color and violet being the shortest. In artificial lighting, the reason why color temperature is used over wavelength or human perception is because of how artificial light sources generate light. Incandescent and radiatory light production methods (incandescent bulbs, fire, etc.) vary in color output based on their physical temperature. When the filament in an incandescent bulb gets hotter, it emits more blue (short wavelength) light and less orange (long wavelength) light. This physical temperature is measured in kelvin, the base unit of temperature, where zero kelvin is absolute zero, approximately -273˚ Celsius and -460˚ Fahrenheit (Abramowitz & Davidson, n.d.).
Spelling of “Streetlight”
There is some debate regarding the proper spelling of the term “streetlight”. Many sources consider the term to be a single word (Cambridge Dictionary; City of San Antonio, TX; Simple English Wikipedia; etc.), while others consider it to be two words (Oxford Learners Dictionary; New York City Department of Transportation; English Wikipedia; etc.). For the purposes of this essay, the noun “streetlight” as well as its verb form “streetlighting” will be considered a single word. The matter of which spelling is correct is not addressed here, and may be worthy of further research by lexicographers.
Traffic Safety
In 2009, the World Health Organization identified all types of motor vehicle crashes, whether they cause no physical harm, injury, or death, as a public health hazard (Gibbons, et al., 2022 p. 2). The National Highway Traffic Safety Administration (NHTSA) reports that of the 100,000 drowsy-driving crashes they count per year, there are approximately 800 fatalities and 50,000 injuries, and that only includes those reported to the police. As for non-reported crashes, the AAA Foundation for Traffic Safety approximates that 328,000 drowsy-driving crashes occur each year with 109,000 resulting in injury and 6,400 resulting in death (National Safety Council [NSC], n.d.).
Staying Awake while Driving
Drowsy driving is an especially large concern at night, when production of melatonin (the hormone produced in the body to induce sleepiness) is at its highest (Gibbons, et al., 2022 p. 1). The trigger that the body uses to determine the start of nightfall (and hence the time to begin melatonin production) is the amount of light the eyes are exposed to. As that amount drops, melatonin levels increase. Artificial lighting of all types disrupts this natural flow (AMA, 2016). Continuous exposure to high levels of light into the night prohibits melatonin production (Gibbons, et al., 2022 pp. 4, 6, 9), and that phenomenon makes streetlights a possible combatant against drowsy driving. An examination of the plasma melatonin levels of people exposed to standard nighttime streetlighting conditions from the perspective of a driver found that melatonin levels sharply declined at the start of exposure (when the participant would begin driving) and stayed low throughout the night. The result was a sharp decrease in feelings of drowsiness (Gibbons, et al., 2022 p. 4).
Color Rendering and Visual Performance
Furthermore, cool white light sources with short-wavelength light generally render colors more similarly to sunlight. This similarity has been shown to help with tasks associated with safe driving, like object identification and depth perception. It also helps to maintain clarity of peripheral vision and allows for greater visual contrast between objects in or along a roadway (Pacific Northwest National Laboratory [PNNL] & U.S. Department of Energy [DOE], 2017 p. 8). The more of this light there is, the safer the roadway conditions are. Studies comparing the rate of crashes in comparison to the illuminance level of the road have found a direct link between the two (Jackett & Frith, 2013 p. 4).
Visual Performance and Tiredness
This would all make it sound as though cooler, brighter streetlighting sources like high color temperature LED bulbs would make for safer roads, however drowsiness and visual acuity are not independent of each other. As human beings stay awake for longer, regardless of their melatonin levels, their degree of visual acuity plummets (AMA, 2016). Melatonin is only an indicator that you should go to sleep, an inducer of a process that needs to happen anyway. Not feeling tired doesn’t mean that you aren’t actually tired, and the more accurate color rendering and contrasting abilities of cool, bright LEDs could conceivably create a falsified sense of safety despite the reduction of visual acuity. Tiredness can also cause an increase in reaction times, exacerbating the core issue (AMA, 2016).
Sleep
In 2016, the American Medical Association (AMA) released the results of a systematic scientific literature review intended to result in a recommendation for proper streetlighting technology. While they touched on various aspects of safety, the more immediate danger they identified was a reduction in sleep quality.
Broad Impacts for All Road Users
The impact of cool, white lights on melatonin production isn’t just limited to drivers, it applies to every single user of the roadway. In this case, that means two primary groups: pedestrians and people living nearby experiencing light entry into their homes (Gibbons, et al., 2022 p. 3). The same study that demonstrated this connection in drivers also identified it in both of these groups (Gibbons, et al., 2022 pp. 6-9). The decrease in melatonin production and the resulting decrease in feelings of drowsiness caused a reduction in overall sleep times for all people exposed to cool white lights. Less sleep has been shown to result in impaired brain functioning and can be a contributing factor to obesity (AMA, 2016). Furthermore, reduced sleep time means excessive drowsiness throughout the day, which can perpetuate the very same traffic safety problem that cool white lights are supposed to help with. However, this allows for the drowsy driving problem to move to the daytime, which may allow for other, defensive drivers to react to a drowsy driver more effectively, resulting in an overall decrease in accidents.
Eye Health Maintenance and Damage
Some preliminary studies have also shown a possible link between exposure to sunlight (which has a spectral distribution similar to that of cool white artificial lights) and a reduction of the likelihood of the development of myopia, also called near-sightedness (Lougheed, 2015). 41.6 percent of Americans suffer from near-sightedness, and it is possible that providing exposure to light that mimics the spectral distribution of sunlight could serve to stave off the onset of myopia in those with healthy eyes. Given that between 1971 and 2017 the percentage of Americans with myopia has gone up by 25 percent (National Eye Institute [NEI], 2017), creating public infrastructure that can combat its onset may not be a bad idea. That being said, studies done on rats have shown that extensive exposure to cool light causes direct retinal damage (Lougheed, 2015), which may outweigh the benefits incurred by the lights on the near-sightedness front.
Pedestrian Safety
To a pedestrian, the most dangerous thing on a roadway is a driver. According to data published by the Insurance Institute for Highway Safety (IIHS) and NHTSA, more than 6,000 pedestrians were killed by drivers on American roads in 2020 (IIHS, 2022). From a driver’s perspective, pedestrians are objects in and alongside the roadway, and hence cool white lights may be able to reduce the rate of collisions between cars and pedestrians via the increase in visual contrast and object recognition these lights provide (PNNL & DOE, 2017, p. 8). There may also be benefits derived from an increase in alertness of both drivers and pedestrians provided by cool white light (AMA, 2016).
Perception of Safety
That being said, it has been found that pedestrians perceive safety differently from other road users. The simple presence of streetlighting is one of the greatest contributors to the perception of safety, and lack of adequate streetlighting can cause people to avoid parks and walkways at night. The fear has nothing to do with the need to be seen by drivers, but instead the need to see potential threats. Furthermore, the feeling of entrapment (or ability to get away in a hurry) is cited as a larger contributor to feelings of safety than lighting of any sort. Things like extensive greenery (which is often considered an aesthetic positive during the day) are key contributing factors to the feeling of entrapment. They create boundaries that restrict the perceived availability of space. Effective streetlighting can break those boundaries by extending visible space, but physical boundaries dull their effectiveness (Rahm, et. al., 2021, pp.5-6). Even if the likelihood of getting hit by a car is greater than the likelihood of being assaulted by a fellow pedestrian, the perceived threat of the latter is more pressing in the minds of individuals.
Davis’ Decision
When any municipality makes a decision, they cannot only consider the facts and merits. They must also consider the way their residents feel. Feelings are powerful in politics, even when those politics are at a local level, because people generally don’t vote on facts alone. The man who wrote the letter to the City of Davis regarding property values wasn’t just referencing some great fact about light and value, but rather the feeling of his neighborhood.
This is what the Davis resident who wrote the letter to the Mayor was talking about: the environment as a whole. Every piece of urban design plays a role in creating a city's “vibe”. The perception of streetlights is just as important to people living in a neighborhood as the safety, efficiency, or health benefits those lights provide. The Davis City Council, and indeed every municipal government around the world, is tasked with something impossible: balancing what the people want and what is best for them. However, neither of those are cut-and-dry measurements. In the end, everything becomes a compromise. In streetlighting, the compromise is made between drivers’ safety, pedestrians’ safety, citizens’ health, visual appeal, and energy-efficiency.
Due to the excess of complaints, the City of Davis stopped the lighting retrofit after only four months. The city worked with residents, and in the end they came to a compromise. The city would get its energy efficiency and the people would get their health and visual appeal via the installation of LEDs set to a color temperature of 2,700K (“Davis, CA LED Streetlight Retrofit”, 2019). What the city had to say, however, was that safety wasn’t as important as looks and money-savings. In order to satisfy the people while still achieving their primary goal, they had to give up morality.
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References
Abramowitz, M., & Davidson, M. (n.d.). The Physics of Light and Color - Color Temperature | Olympus LS. https://www.olympus-lifescience.com/en/microscope-resource/primer/lightandcolor/colortemp/
American Medical Association. (2016, June 14). AMA adopts guidance to reduce harm from high intensity street lights. https://www.ama-assn.org/press-center/press-releases/ama-adopts-guidance-reduce-harm-high-intensity-street-lights
Bullough, J., Rea, M., & Akashi, Y. (2009). Several Views of Metal Halide and High-Pressure Sodium Lighting for Outdoor Applications. Rensselaer Polytechnic Institute Lighting Research Center. Retrieved March 22, 2023, from https://web.archive.org/web/20100609221917/http://www.lrc.rpi.edu/programs/transportation/projects/OutdoorLightingTypes.asp
Archived
Davis, CA LED Streetlight Retrofit - Smart Outdoor Lighting Alliance. (2019, March 4). Smart Outdoor Lighting Alliance. https://volt.org/lessons-learned-davis-ca-led-streetlight-retrofit/
European Commission. (n.d.). Are LED lights safe for human health? European Commission - Public Health. https://health.ec.europa.eu/scientific-committees/easy-read-summaries-scientific-opinions/are-led-lights-safe-human-health-0_en
Gibbons, R. B., Bhagavathula, R., Warfield, B., Brainard, G. C., & Hanifin, J. P. (2022). Impact of Solid State Roadway Lighting on Melatonin in Humans. Clocks & Sleep, 4(4), 633–657. https://doi.org/10.3390/clockssleep4040049
Greenwald, D. (2014, May 27). The City’s Streetlight Retrofit Project Draws Complaints. Davis Vanguard. https://www.davisvanguard.org/2014/05/the-citys-streetlight-retrofit-project-draws-complaints/
Insurance Institute for Highway Safety. (2022, May). Fatality Facts 2020: Pedestrians. IIHS-HLDI Crash Testing and Highway Safety. https://www.iihs.org/topics/fatality-statistics/detail/pedestrians
Jackett, M. J., & Frith, W. J. (2013). Quantifying the impact of road lighting on road safety — A New Zealand Study. Iatss Research, 36(2), 139–145. https://doi.org/10.1016/j.iatssr.2012.09.001
Lougheed, T. (2014). Hidden blue hazard? LED lighting and retinal damage in rats. Environmental Health Perspectives, 122(3). https://link.gale.com/apps/doc/A363973864/AONE?u=plan_skyline&sid=bookmark- AONE&xid=c0e58e66
National Eye Institute. (2017, October 3). Myopia: A close look at efforts to turn back a growing problem. https://www.nei.nih.gov/about/news-and-events/news/myopia-close-look-efforts-turn-back-growing-problem
National Safety Council. (n.d.). Drivers are Falling Asleep Behind the Wheel. https://www.nsc.org/road/safety-topics/fatigued-driver
Pacific Northwest National Laboratory & U.S. Department of Energy. (2017, February). Street Lighting and Blue Light - Frequently Asked Questions. U.S. Department of Energy. Retrieved March 22, 2023, from https://www.energy.gov/sites/prod/files/2017/03/f34/Street%20Lighting%20and%20Blue%20Light%20FAQs.pdf
Rahm, J., Sternudd, C., & Johansson, M. (2021). “In the evening, I don’t walk in the park”: The interplay between street lighting and greenery in perceived safety. Urban Design International, 26(1), 42–52. https://doi.org/10.1057/s41289-020-00134-6
Schivelbusch, W. (1995). Disenchanted Night: The Industrialization of Light in the Nineteenth Century. University of California Press.
Sharp, R. (2014, August 19). Davis asks residents to rank new LED street lights. KCRA. https://www.kcra.com/article/davis-asks-residents-to-rank-new-led-street-lights/5957176
Stevens, R. G. (2016, June 21). Doctors issue warning about LED streetlights. CNN. https://www.cnn.com/2016/06/21/health/led-streetlights-ama/index.html
Uttley, J., Fotios, S., & Lovelace, R. (2020). Road lighting density and brightness linked with increased cycling rates after-dark. PLOS ONE, 15(5), e0233105. https://doi.org/10.1371/journal.pone.0233105