Street lights effect on buildings / landscape design, trees, wildlife,  circadian rhythms and health / well-being

CIBSE Technical Symposium
Stretching the envelope: Techniques, applications and technologies for healthy and productive environments
London 2018 – Thursday 12th – Friday 13th April

David Garlovsky, BSc, MSc, Certificate in Social Phenomenology, Certification in Focusing Affiliation: Schools & Homes Energy Ed. Project/Solar-Active / Recovery Insulation
84 Upper Valley Road, Sheffield S8 9HE, United Kingdom


Urban and rural areas in UK and elsewhere for past several years are changing over roadway and residential street lighting from high pressure sodium [HPS] to blue-rich LED’s often simply on the basis of saving energy but without health and environmental impact assessments. Research has shown that making choices simply on the basis of energy consumption is shortsighted. Research has shown that blue-rich LED’s affect human health and wellbeing in having an impact on people’s ability to get a good night’s sleep, circadian rhythms, road safety and view of the night sky. It is crucial for policy makers to link LED installation to heath, ecology considerations and involve local communities in deciding how streetscapes including trees and lighting are planned, managed and maintained.

Key words: blue-rich LED’s, circadian rhythms, human health & wellbeing, road safety and night sky


The views presented in this paper are from a historical perspective based on research conducted by the author and others in the City of Chicago in 1974/75. A literature review was also conducted 2012-17 with a focus on installation of high pressure sodium [HPS] lamps and blue-rich LED’s blue-rich effect on buildings/landscape design, human health and wellbeing, wildlife, circadian rhythms, road safety and the view of our night sky. This paper is building upon the research published in Let There be Darkness published 4th December 2017. (Garlovsky, 2017)i

As a resident and Environmental Education Teacher/Trainer with the District 14 Education Council of the Chicago Board of Education, in the 1970’s the author first became interested in the effects of security street lighting on residential street trees, wildlife and humans when planting trees and shrubs in an around school buildings.

In the review of City of Chicago records and local newspapers it was discovered that every four years, and always in an election year, the City of Chicago elected politicians’ (i.e. Ward Alderman) wished to be seen to address the primal fear of darkness by replacing residential security street lighting systems.

Their decision in 1974 to replace 400-watt High Pressure Sodium [HPS] lamps was primarily based on being advised that HPS lamps would save energy and have no harm to trees from the recommendation of their appointed paid consulting arborist. As a result legislation to purchase the HPS lamps was passed at the City Council meeting held in July 1974. It was perceived by residents that the city was taking proactive steps to address their fear of darkness and reduce crime.

It was found that the arborist’s recommendations were simply based on two weeks’ observation of 210 trees in Chicago, Cleveland, and Milwaukee and on telephone interviews with officials in 16 cities in U.S.. Research in 1974/75 by the Chicago Audubon Society [CAS], M. Ruddat, of the University of Chicago, Department of Ecology and Evolution, Biological Sciences Collegiate Division and Chicago District 14 Environmental Education Project considered the report inadequate by the arborist (Ruddat, 1975) ii

CAS questioned the consulting arborist sampling procedure that showed that mature trees compromised 90% of his sample, however, the young trees being planted would be most vulnerable. CAS also questioned the value of the arborist observations or conversations, indicating that there were no harmful affects due to HPS lamps. The field surveys by CAS conducted showed that 11% of the HPS lamps after 13 months failed.

The surveys also observed and recorded the affects of the HPS lamps on the young trees being planted, with 60% of a group of saplings suffering death or damage to growth over their first spring and summer. In addition, at the Chicago avenue site 16 honey locusts were planted. It was found that 10 of these young trees were dead or damaged. All 16 trees were eventually felled that of course affected our study. (Ruddatt, 1975) iii

Figure 1 Leaf hold near HPS lamp

It was also observed that young trees growing under the HPS lamps were 8 times more likely to be holding their green leaves at the time of first killing frost than those growing under Mercury Vapour lamps. As a result the young trees became vulnerable to frostbite. The HPS lamps also had a bad effect on privet, roses and chrysanthemums. It was observed a breaking of dormancy in December of hybrid and wild rose specimens, privet, pachysandra and chrysanthemums within 15 feet of the light standards. (Gewirth, 1973) iv

A report of the analysis of our surveys in Chicago was presented at a private meeting of the City of Evanston (that boarders the northern boundary of City of Chicago) elected councillors and officers. Based on our report it was decided not to install the HPS lamps on Evanston’s residential streets.

The effect of artificial light on trees is not a newly discovered problem. Botanists were aware of deleterious affects of incandescent street lighting on trees 81 years ago by Matske in 1936. (Matske, 1936)v, while horticulturalists became aware as result of research 42 years ago by Cathey and Campbell in 1975 with harmful affects on both wild and domesticated plants. (Cathey, 1975). vi

Transition from HPS lamps to blue-rich LED’s

Urban areas in UK and elsewhere are changing over roadway and residential street lighting from HPS lamps to cool-white blue-rich LED’s at an alarming pace during the past several years. The rush to replace roadway lighting systems with blue-rich LED’s is a real cause for concern and needs to be urgently addressed.

Funding for this change over to blue-rich LED’s in UK was encouraged by UK Technology Strategy Board (TSB) Future Cities Demonstrator programme with a focus on wireless technology to provide more efficient roadway security lighting while reducing energy consumption and cutting CO2 emissions. For example, Westminster City Council installed warm 2700K white Luxeon LEDs in 2006. (TSB, 2014)vii

New research shows, this solution hasn’t yielded the expected energy savings, and resulted in more light pollution than ever before. (Falchi, et al, 2016)viii Even though research recognised that blue-rich LED is detrimental to human and causing circadian disruption.

A large body of research has shown that making choices about the kind of lights we use on our residential streets and roadsides, simply on the basis of energy consumption is shortsighted. The analysis of research has shown that by changing urban lighting from HPS lamps to blue-rich LED’s “we may – and again, the emphasis is on may – be upsetting the ecological balance in unexpected ways.” (Ashdown, 2016) ix

A National Lighting Policy Is needed, including strict guidelines curtailing blue-rich LED light pollution. UK Government grants for installing blue-rich LED streetlights urgently needs to be halted until further environmental assessments are completed. For instance, Energy saving measures need also to be linked to health and ecology considerations such as the presence of heavy metals in LED’s in their manufacture. A study published in late 2010 in Journal Environmental Science and Technology found that LED’s contain lead, arsenic and a dozen other potentially dangerous substances. Oladele Ogunseitan one of the researchers behind the study stated we must be vigilant about any toxicity in supply chain of these products. (Seong-Rin, 2012)x

The environmental threats of artificial light

Pollinators are declining worldwide and this has raised concerns for a parallel decline in the essential pollination service they provide to both crops and wild plants. The rapid global increase in artificial light at night is a new threat to terrestrial ecosystems as artificial light at night disrupts nocturnal pollination networks. In artificially illuminated plant–pollinator communities, nocturnal visits to plants were reduced by 62% compared to dark areas. (Knop, 2017)xi

Excessive outdoor lighting disrupts many species that need a dark environment. Poorly designed LED lighting disorients some bird, insect, turtle and fish species. Knowing this the U.S. national parks has adopted optimal lighting designs and practices that minimize the effects of light pollution on the environment. (AMA, 2016)xii

LED’s effect on road safety and sky glow

A study of pictures of Earth by night has revealed that artificial light is growing brighter and more extensive every year with unintended consequences for human health and the environment. (Falchi, 2016)xiii Blue-rich LED streetlights are also a nemesis to astronomers due to unacceptable levels of light pollution due to excessive glare caused by the “Rayleigh Scattering Effect”. (Ashdown, 2015)xiv Two studies have also concluded that to focus simply on CCT LED’s to reduce Sky Glow misses the problem, as it is caused by all of the white LED sources. (Luginbuhl, 2012; Aube, 2013) xv

Blue-rich LED’S have been shown to double driver peripheral vision and increase brake reaction time by 25%. (Mokoff, 2015)xvi ‘Modern’ headlights (without automatic adjustment-system) and street lamps are causing glare and prolonged retinal recovery following light ‘stress’. (NHTCA, 2007) xvii

Nighttime Crime

Many believe improving visibility will have an effect on nighttime crime including sexual assault. When there is no outdoor lighting, pedestrians may genuinely feel fear. Simply being able to see makes us feel safer. However, feeling safe and actually being safe are not the same. There is no clear scientific evidence that increased outdoor lighting deters crimes. It may satisfy the “feeling of safety”, but has not been shown to make us safer as confirmed by one of the largest, most scientific studies of outdoor crime and lighting at night in the 1998-99 Chicago Alley Study (Morrow, 2000)xviii and was also confirmed in other cities. (Steinbach, 2015)xix

Feedback from Chicago residents was mostly positive; the only problem was that the residential light replacement program did not reduce crime. To the contrary, in the areas where “enhanced lighting” was installed, incidence of crime increased. Studies in the UK comparing communities with similar demographics in which the only difference was the introduction of street lighting have found no significant variation in the rates of crime. (Parks, 2014) xx

CCT (correlated color temperature) LED’S of 2700K (Kelvin)

It is wildly now accepted that in the lighting of streets, roads and other outdoor public places should ideally have a CCT of 2700K – but in any event must not exceed a CCT of 3000K. (Bunya, 2015)xxi

The City of Davis California in 2015 replaced newly installed 4800K with 2700K at a cost of $350,000 following surveys that showed residents complaints about what they called “prison-white lighting. (Ashdown, 2015) xxii The U.S. Department of Energy published a Gateway report Pedestrian Lighting. Had city officials acted on the report, they might have saved $350,000 and the wrath of the citizenry. (DOE, 2014)xxiii

The city of Montreal’s LED streetlights project suspended its $110 million project to replace 110,000 standard streetlights with LED lighting until the health risks and potential for light pollution of the new technology is better documented. (Bruemmer, 2016) xxiv

The Cardiff City Council opted for 3000K after Public Trials and Consultations. It is using Philips Lighting to switch to LED lighting. It has estimated the City can reduce electricity consumption by up to 60% and save the council more than £750,000 per year. It will also contribute to the goal of reducing CO2 emissions. The exercise the council undertook identified a preference away from blue-rich LED’s light at 5,000 Kelvin to a warmer light of 3,000 Kelvin. By utilising 3,000 Kelvin LED lights the light will match the streetwise lanterns placed during the dimming contract. This will provide a unified light colour and temperature across the City. (Marr, 2016)xxv

Yet, in contrast, the Sheffield City Council (SCC) are installing 5000K LED’s and has taken no notice of the U.S. Department of Energy Gateway report Pedestrian Lighting and other research. Nor have they taken advise of the AMA (American Medical Association), IDA (International Dark Sky Association), CPRE (Campaign for Rural England) and PHE (Public Health England) that are all recommending to use warm-white CCT – ideally 2700K lights to minimize glare and discomfort. (Stevens, 2016)xxvi

Sheffield council signed away its powers when it signed a PFI contract with Amey (owned by Ferrovial, one of the world’s leading infrastructure operators and municipal services companies.) Sheffield’s citizens have found it difficult to influence their elected council, which is accountable only to Amey, The nature of PFI contracts is an issue that extends well beyond Sheffield and its trees. (The Huffington Post, 2017) xxvii The SCC, tree campaign and media need to focus on facilitating constructive communication between themselves for the benefit of the residents of Sheffield.

The International Dark Sky Association recommends a CCT of maximum 3000K. The Isle of Wight Council is trying to attain Dark Skies status. It would be a much smoother process if they changed to warm CCT lights. It is critical that the Island Lighting Code includes strict guidelines on CCT, where 3000K should be the absolute maximum and downward directing. The Island lights are currently 5700K but how they will change to 3000K is uncertain. Apart from being an improvement on Sky Glow, warm colour temperature light is also better for humans and wildlife, as it doesn’t disrupt circadian rhythms as much as blue-rich light.

Street lighting and human health & well-being

Light affects our health and well being in more ways than one. LED based streetlights are whiter than traditional ones and contain more blue light, which can disrupt people’s circadian rhythms. Dr. Anna Weighhall states as the world is getting brighter at night due to artificial light, the LED light has the potential impact on people’s ability to get a good night’s sleep. (BBCRadio4, 2017).xxviii ‬‬

Studies recognized by the World Heath Organization [WHO] show blue-rich LED’s emit a form of blue light that suppresses the production of melatonin, responsible for regulation of the body‘s biological clock. Interference with the body’s internal clock has been associated with health problems including sleep disruption, depression, diabetes, obesity and cancer. (Stevens, 2016) xxix

The American Medical Association (AMA) at their annual meeting, 14th June 2016 adopted an official policy statement about street lighting: “cool it and dim it”. This was in response to the rise of new LED street lighting sweeping the country. An AMA committee issued guidelines on how to choose LED streetlights to minimize harmful human health and environmental effects. Although the streetlights deliver energy saving benefits, the AMA’s stance reflects how important proper design of new technologies is and the connection between light and human health. (AMA, 2016) xxx

The AMA has three recommendations: First, supports a “proper conversion to community based LED lighting, to reduce energy consumption and decreases use of fossil fuels.” Second, “encourage[s] minimizing and controlling blue-rich environmental lighting by using the lowest emission of blue light possible to reduce glare.” Third, “encourage[s] the use of 3000K or lower lighting for outdoor installations. All LED lighting should be properly shielded to minimize glare and detrimental human and environmental effects, and consideration should be given to utilize the ability of LED lighting to be dimmed for off-peak time periods.” (AMA, 2016) xxxi


Researchers have found that in a typical urban area with high levels of air pollution, an extra 300 trees per square kilometre was associated with 50 fewer emergency asthma cases in every 100,000 residents, however this association varied by pollutant exposure. Air pollution is the ‘tobacco of the 21st century’, warns expert Dr. Ian Alcock of University of Exeter’s Medical School. (Alcock, 2017)xxxii

Research at University of Manchester has shown that urban trees intercept airborne particles, reducing pollution levels, provide shade (cooled urban populations by up to 4-7°C and surfaces by 15-20°C) and cooling and intercept rainfall, reducing runoff by 60%, and the chances of surface flooding. The research also highlighted deficiencies in our knowledge about urban trees. The results suggest that tree surveys that measure tree growth rate and record-planting conditions could vastly improve our knowledge of the value of trees in our towns. (Armson, 2012)xxxiii

These findings hopefully will have important implications for public policy as the study supports growing evidence that “the respiratory health of populations in highly polluted urban areas can be improved by the expansion of tree cover.” (Matthews-King, 2017)xxxiv It comes as National Audit Office report showed 85 per cent of the UK’s “clean air zones” are still in breach of legal air pollution limits, eight years after they were supposed to be hitting targets. (National Audit Office, 2017)xxxv

Following a request from the European Commission, the Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) reviewed recent evidence to assess potential risks to human health of blue-rich LEDs and has identified gaps in knowledge on potential risks to human health. For instance, children have a higher sensitivity to blue light and although emissions may not be harmful, blue-rich LEDs (between 400 nm and 500 nm) may induce photochemical retinopathy, which is a concern especially for children below three years of age. Elderly population may experience discomfort with exposure to LED systems, including blue-rich LED displays e.g. destination displays on the front of buses will be blurred). (SCHEER, 2017)xxxvi

Peter Boyce, professor of lighting and human factors wrote that there are three kinds of lighting: bad lighting, nondescript lighting and good lighting. Bad lighting, which has identifiable faults, should be avoided and the new blue-rich LED lamps have faults: glare, light trespass and colour temperature. (Boyce, 2014)xxxvii

How LED’s will effect day length may affect building landscape design, vegetable gardens and soybean farmers

LED lighting can have an effect on the short day/ long night plants, which flower in spring or fall. A plant that requires a long period of darkness is termed a “short day” (long night) plant. Short-day plants form flowers only when day length is less than about 12 hours. Many spring and fall flowering plants are short day plants.

Table 1: Long, short and day neutral plants

Long Day/short night Plants
(Day Length > 12 hrs)
Flower in summer
Short Day Plants
(Day Length < 12 hrs)
Day Neutral Plants
(Ignores Day Length)
Artichoke & lettuce & spinach black-eyed peas apples
Barley & oats blueberries apricots
beets & onions & radishes cotton brussels sprouts
Cilantro & potatoes raspberries corn
dill & rye & grass & asters soy beans kale
flax & turnips & hollyhocks sweet potatoes pears
lentil & wheat rice tomatoes

Almost all living things have an internal circadian clock that controls many of life’s processes within every cell. Sensitivity to day length (photoperiodism) determines when a plant bolts, fruits or produces storage organs. It is the length of the dark periods that controls plant growth. According to University of Washington researcher Takato Imaizumi, “The circadian clock is not constantly sensitive to light. It has a light-sensitive window at the end of the day that acts as a gating mechanism.” Long-day plants want to flower as we move toward the longest days of the year. Short-day plants want to flower earlier in spring or in fall. There are plants that disregard the day length and determine their flowering on factors such as temperature or the stage of maturity. These types are called day-neutrals. (Imaizuni, 2006)xxxviii

For instance, since soybean is a short-day plant, soybean farmers learned not to plant in a field adjacent to HPS roadway lighting. The night time illumination can reduce crop yield by 20 to 40%. (Chen, 2009)xxxix

Artificial street lights can be injurious to most trees and be fatal to young ones

Horticulturalists became aware of the problem as a result of research using 40ornamental trees some forty years ago conducted by Cathey and Campbel in 1975 at U.S. Agriculture department center in Beltsville. They found that artificial security lights can be injurious to most trees and be fatal to young ones. It was found that species of trees exhibit intermediate or low growth responses to the security lighting. When compared the 5 light sources used promoted vegetative growth and delayed dormancy of the woody trees in the order from most to least effective. (Cathey, 1975) xiv. Figure 2 shows a Birch with a dead crown planted near HPS lamp on 55th and Woodlawn in Chicago,

Figure 2 showing a Birch near HPS lamp with dead crown

The sensitivity of the 40 trees to security lighting were then placed into three groups i.e. High, Intermediate and Low. Betula papyrifera (Paper birch) was in the high group. Table 2 below shows the sensitivity of 40 plants to security lighting. Plants have been listed alphabetically and are not grouped in descending order of sensitivity. A high, intermediate, or low rating identifies the relative responsiveness of the plants to security lighting.

Table 2: Sensitivity of 40 plants to security lighting

High Intermediate Low
Acerginnala, Amur maple Acerrubrum, Red maple Fagus sylvatica, European beech
Betula papyrifera, Paper birch Cercis canadensis, Redbud Carpinus japonica, Hornbean
Betula pendula, European white birch Cleditsia triacanthos, Honeylocust Ginkgo bilola, Cinkgo
Betula populifolia, White birch Cornus controversa, Giant dogwood Ilex opaca, American holly
Platanus aceriiolia, Sycamore Ostryavirginicana, Ironwood Malus boccata, Siberian crabapple
Ulmus americana, American elm Tilia cordata, Littleleaf linden Quercus robur, English oak

It is red light from streetlights that is the problem and can have harmful effects on both wild and domesticated plants. Depending on the species and various environmental factors, even low levels of light trespass from roadway and outdoor luminaires can have harmful effects. LED streetlights likewise emit more red light on a per lumen basis than HPS street lights. Sensitivity of trees, distance from lamp standard, season, temperature and age are factors that need to be considered.

The specific band of wave lengths of light tells a tree or shrub to grow while through shorter days and cooler nights, mother nature is telling it to get ready for winter. Trees prepare for winter by becoming dormant. Come a cold snap, a young tree still growing could be killed.

LED streetlights likewise emit more red light on a per-lumen basis than HPS lamps. For example, “It is the specific band of wave lengths at the red end of the spectrum that were the controlling factor in preventing morning glory buds from opening normally”. (Ott, 1958) xivii

Scientific research has confirmed it is the length of the dark periods that controls plant growth. Almost all living things have an internal circadian clock that controls many of life’s processes. According to University of Washington researcher Takato Imaizumi, whose Imaizumi Laboratory studies seasonal response and circadian rhythms in plants, “The circadian clock is not constantly sensitive to light. It has a light-sensitive window at the end of the day that acts as a gating mechanism. (Imaizuni, 2006) xivii

The Chicago research in 1974/75 by the Chicago Audubon Society and M. Ruddat, of the University of Chicago, and the literature researches between 2014 -17 have found that excessive outdoor lighting disrupts many species in the wild and urban environs that need a period of a darkness for their health and well being.

Poorly designed LED lighting disorients some bird, insect, turtle and fish species. Knowing this, US national parks have adopted optimal lighting designs and practices that minimize the effects of light pollution on the environment and the same needs to happen in UK and elsewhere. (AMA, 2016) xiviii

The wavelength, angle and intensity of new or replacement lighting intended to save energy should be tested in situ before a scheme is implemented to ensure that it is the minimum required and does not cause harm to human well-being, trees and wildlife and be preceded by thorough Health and Environmental Impact Assessments. 


Trees can significantly influence the urban environment. Further research is needed to quantify and monetise better the environmental benefits of urban forest ecosystems and to quantify their effects for our health and wellbeing. City officials need to be urged to carefully select trees that are unaffected by the blue rich LED’s without creating a monoculture of trees on the urban streets.

UK needs to create a National Lighting Policy with responsible standards to guide urban and outdoor lighting design and not continue to allow uncontrolled lighting in their rush to replace roadway lighting systems with blue rich LED’s. These practices are degrading the quality of life and have a negative impact on human health and ecology adding to the breakdown in connectivity between people and nature. A better understanding of how and to what degree urban trees influence the environment will lead to better management of urban trees, significant monetary savings for urban residents and a more pleasant and healthy urban environment.

There is almost never a completely satisfactory solution to a complex problem. We must have lighting at night, not only in our homes and businesses, but also outdoors on our streets. The need for energy efficiency is serious, but so too is minimising human risk from bad lighting, both due to glare and to circadian disruption. LED technology can optimise both when properly designed.

In UK Forestry Commission found that “research on street trees is sparse.” Research is needed with the participation of local authorities, arboriculturalists and tree owners to understand better the social and cultural values associated with street trees in order to implement current, future policy priorities and write new legislation related to climate change adaptation to better protect existing trees and generate better planting that is needed by tomorrow’s urban communities. (Norman, 2010) xiviv

It is imperative for local communities be listened to and involved in deciding how streetscapes including trees and lighting are planned, managed and maintained to ensure that citizen concerns and complaints about excessive lighting are taken seriously and demand action. Tree planting initiatives involving community members, would be of value relating for communities to participate in the process.


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