Crime, Safety and the Social Justice Aspects of Light Pollution

This blog post draws heavily on “The State of the Science” report by John Barentine, available here.


The belief that outdoor lighting improves traffic safety and discourages or prevents crime is common. It may explain in part the rapid growth in the use of outdoor light at night in recent years and decades. There are cases where the careful application of outdoor lighting may improve night-time safety, but there is no general benefit supported by scientific evidence.

Crime, Safety and Traffic

There is conflicting research on this topic and no consensus that adding or increasing lighting reduces crime, or traffic accidents, (except on busy urban junctions, where sensible lighting is shown to reduce accidents.)

Researchers have not been able to accurately predict or model the way that lighting might affect actual crime figures.  There are issues with the scientific reliability and honesty of that show a reduction in crime rates where lighting is installed, e.g. one study concluded that putting additional lighting did reduce crime, but the researchers failed to report that in those areas, additional policing was also implemented, which was not in the areas with no or low lighting.

Confounding factors and variables have subtle effects on research that add up to important, erroneous conclusions because responsibility can easily be assigned to lighting even though it contributed very little.  As a result, many of the claims about outdoor lighting and its impact on crime and traffic safety – for better or worse – may be fundamentally wrong (266, 267).

The Hazards of Glare

Glare from bright artificial light sources can decrease night-time safety.  Intense light directly entering the eye from unshielded sources scatters inside the observer’s eye, reducing the contrast between foreground and background and reducing peripheral and night vision.  Additionally, the pupil of the observer’s eye contracts, reducing total visibility by dimming the appearance of the entire scene. These effects make it difficult to see objects, such as cars or potential attackers, as distinct from what surrounds them.

Are We Afraid of the Dark?

Although the data on crime statistics is variable, how we feel about crime in relation to the darkness is not.  People in Western, urban societies tend to feel safer when there is more light, but how much more is needed for this effect?  The amount of light used in outdoor spaces at night may not reflect public expectations for feelings of safety and comfort (270), and artificial light itself may influence the human perception of fear (271). In some cases, over-lighting can itself become the source of safety hazards (272). However, properly designed lighting can reduce light pollution and save energy without compromising on public feelings of safety in outdoor spaces at night (273).

Conclusions for Crime and Safety.

The assumption that adding bright lights reduces crime is not supported by evidence.  However, adding appropriate, sensible, thoughtful lighting does reduce our fear of crime at night, and also reduces the obvious safety issue of glare.

Lighting and Social Justice

We know very little about how light pollution affects people in social contexts. Light at night may be used in ways that affect neighbourhoods according to the race of the people who live in them. That may make light at night use a matter of social and environmental justice.

Light Pollution, Racism and Poverty

The only comprehensive study to date on this topic looked at the social aspects of lighting in the U.S. only (292). Researchers found that Americans of Asian, Hispanic and Black descent tend to live in brighter neighbourhoods (Figure 7). In these areas, skyglow is about twice as Figure 7. Average exposure to light pollution in the continental United States by racial/ethnic group. The bars show population-weighted average zenith night sky brightness levels in units of millicandelas per square meter. Figure 4 in Nadybal, Collins and Grineski, 2020 (292). high as in predominantly white neighbourhoods. They further note that lower socioeconomic status is also associated with higher night-time light exposures. These conditions can add to other social and environmental stressors such as poverty and exposure to air and water pollution, affecting quality of life.

Closely related to this is the idea that light pollution is harmful to people whose religious or cultural practices rely on access to the night sky. The erasure of the stars from view due to skyglow separates people from this resource. Some argue that it threatens Indigenous traditions and knowledge systems based on accessibility of the natural night sky (300).


  • Marchant, P. Why lighting claims might well be wrong. International Journal of Sustainable Lighting, 19(1):69–74, jun 2017. doi: 10.26607/ijsl.v19i1.71.
  • Marchant, P. Do brighter, whiter street lights improve road safety? Significance, 16(5):8–9, oct 2019. doi: 10.1111/j.1740-9713.2019.01313.x.
  • Svechkina, A., Trop, T. and Portnov, B.A. How much lighting is required to feel safe when walking through the streets at night? Sustainability, 12(8):3133, apr 2020. doi: 10.3390/ su12083133.
  • McGlashan, E.M., Poudel, G.R., Jamadar, S.D., Phillips, A.J.K. and Cain, S.W. Afraid of the dark: Light acutely suppresses activity in the human amygdala. PLOS ONE, 16(6): e0252350, jun 2021. doi: 10.1371/journal.pone.0252350
  • Marchant, P., Hale, J.D. and Sadler, J.P. Does changing to brighter road lighting improve road safety? multilevel longitudinal analysis of road traffic collision frequency during the relighting of a UK city. Journal of Epidemiology and Community Health, 74(5):467–472, mar 2020. doi: 10.1136/jech-2019-212208.
  • Saad, R., Portnov, B.A. and Trop, T. Saving energy while maintaining the feeling of safety associated with urban street lighting. Clean Technologies and Environmental Policy, 23 (1):251–269, nov 2020. doi: 10.1007/s10098-020-01974-0.
  • Nadybal, S.M., Collins, T.W. and Grineski, S.E. Light pollution inequities in the continental united states: A distributive environmental justice analysis. Environmental Research, 189: 109959, oct 2020. doi: 10.1016/j.envres.2020.109959.
  • Hamacher, D.W., de Napoli, K. and Mott, B. Whitening the sky: light pollution as a form of cultural genocide, 2020.
The milky way in Autumn over the roof of Battlesteads Observatory

The Big Switch Off.

The Big Switch Off of lights across Ambleside and Grasmere is happening again this year on Thursday 23rd February, from 7pm.

Following the success of two previous events, street lights will be turned off and businesses and residents are encouraged to take part by turning their own lights off.

Too many lights are left on overnight when not needed, wasting energy, adding to electricity bills and releasing more carbon emissions into the atmosphere.  Artificial light at night is also harmful to wildlife, can damage people’s sleep patterns affecting long-term health, and creates light pollution when too bright or badly fitted.

Lots of local businesses, residents and organisations in Ambleside and Grasmere are taking part, including hotels and B&Bs, St Mary’s Parish Church Ambleside, Ambleside and Grasmere Primary schools, and lots of householders.

Friends of the Lake District’s Dark Skies Cumbria Officer, Jack Ellerby, said: “Last February the clear skies gave a really impressive show of thousands of stars after all the lights went off. I talked to visitors and residents out and about and they were so pleased to have the opportunity to see so many stars. This year we’ve created a ‘Dark Skies room brochure’ leaflet for accommodation business guests to encourage them to step outside, look up and be wowed by how many stars they can see.” Read more about the Dark Skies Room brochure here.

Please do join in with the Big Lighting Switch Off on 23 February and come along to enjoy the evening experience.

Gillian Kelly, of Ambleside Action For A Future, said:

“The annual Big Switch Off is about encouraging all of us to reduce the wasteful use of energy, to ask ourselves, do we really need so many lights on all through the night? Seeing lots of lights go off is a highly visible way of getting the broader messages across to safeguard climate stability and help to reverse the severe declines to our threatened wildlife. Lots of individual small actions add up to make a collective improvement for people and the planet.”

Huge thanks to Cumbria County Council’s lighting team for making the event such a success by switching off road and street lights, plus Ambleside Action For A Future, Grasmere Village Society, Lakes Parish Council and South Lakeland District Council, who’ve all worked together with Friends of the Lake District Dark Skies on the Big Switch Off initiative.

The Big Switch Off takes place during Annual Star Count Week (17-24 February 2023), run by the CPRE, The Countryside Charity, asking people to take part counting the number of stars they can see in the Orion Constellation to help monitor light pollution trends in Cumbria and across England. Read more about the Star Count here.



light from streetlights pours into a house on the staircase through a window

Sleep and Light Pollution

For thousands of years, humans have lived a 24-hour day marked by the rising and setting of the sun. We have evolved to respond to the blue parts of sunlight, regulating our waking and sleeping cycle. Most artificial light reduces our ability to see the starry night sky, but it also impacts our sleep-wake cycles, or circadian rhythms. These circadian rhythms are universal across bird, reptile, and mammal species

Unfortunately, in our modern day-to-day life, light pollution extends our “daytime” experience well past sunset, thanks to artificial lighting containing some fraction of blue light.

Sleep is Essential

Everyone is a big fan of a good night’s sleep, but as you can see, sleep is an essential part of your wellbeing and health.


Melatonin is a key chemical related to your circadian rhythm and is strongly linked to getting you ready for sleep.

In animals, melatonin plays an important role in the regulation of sleep–wake cycles.[18] Human infants’ melatonin levels become regular in about the third month after birth, with the highest levels measured between midnight and 8:00 am.[19] Human melatonin production decreases as a person ages.[20] Also, as children become teenagers, the nightly schedule of melatonin release is delayed, leading to later sleeping and waking times.[21]


Blue light prevents your body from making melatonin which can cause insomnia or prevent you falling asleep at the right time.

Light Pollution and Sleep – The Science Bit.

Think of a rainbow; can you remember all the different colours there are? We are interested in how the blue part of a light spectrum (or rainbow) affects our sleep. It turns out that the eye contains a part that is specifically for synchronising your circadian rhythm. These “ipRGC” cells react to blue light, and when they activate they send a signal to the brain that stops it producing melatonin. So if you want a good nights sleep, and if we want the animals in our habitats to sleep well, we MUST tackle the “blue light” part of our lighting at night.

For you, the best thing you can do is use a blue light filter, or “comfort filter” on your mobile phone. You can check the colour temperatures of your light bulbs and make sure they are less than 3,000K, the lower the better.  (Smart lights are great, e.g. Hue, because you can set them to any colour temperature you like, for example if you have Hue lights and a google hub you can say “Ok Google, set my lights to two thousand kelvin” – try it and see!) Research on melatonin suppression due to blue wavelengths of light is available if you click here.

Red Light and Sleep

There is some evidence suggesting that red, or redder lights at twilight and night can help you fall asleep, (although other evidence suggests its the absence of blue light that acts as a passive influence.)  In either case, your brain releases more melatonin as darkness falls and tends to release less when you’re exposed to blue light.  The bottom line is that we need to sleep in complete darkness, and to avoid as much exposure to light of all colours in the hour or so before we want to nod off.

The Milky Way and several dark sky objects such as Orion and the Pleiades over Battlesteads Observatory in Northumberland


The Milky Way and several dark sky objects such as Orion and the Pleiades over Battlesteads Observatory, illuminated with red light, in Northumberland. Image: Dr Martin Kitching

In a 2012 study on 20 female athletes, participants were randomly given 30 minutes of red light therapy every night for two weeks. When compared to the placebo group with no light therapy, the athletes had improved quality of sleep, melatonin levels, and performance. In 2019 a 3-week study of 19 people in an office environment showed that using a combination of red with the office white light in the afternoon improved afternoon alertness and circadian rhythms. There is growing evidence that red light plays a role in triggering melatonin production at night (maybe because we evolved over the centuries watching beautiful orange/red sunsets?)

Red Light and Sleep Inertia

The Angel of the North in Gateshead is viewed looking West on a cloudy day at sunset. A couple are sharing an intimate moment as they watch the sun set.


An Intimate Moment with The Angel of the North at Sunset by Roy Alexander

Sleep inertia is a sleepy feeling that you feel after you wake up. It can affect your short-term memory and alertness. A small 2019 study on sleep inertia showed that saturated red light delivered through closed eyelids, at levels that don’t suppress melatonin, may help ease sleep inertia when we wake up.

Wildlife & Ecosystems

For billions of years, all life has relied on Earth’s predictable rhythm of day and night. It’s encoded in the DNA of all plants and animals. Humans have radically disrupted this cycle by lighting up the night.

When we add light to the environment, that has the potential to disrupt habitat, just like running a bulldozer over the landscape can.”

— Chad Moore, formerly of the National Park Service

Plants and animals depend on Earth’s daily cycle of light and dark rhythm to govern life-sustaining behaviours such as reproduction, nourishment, sleep and protection from predators.

Scientific evidence suggests that artificial light at night has negative and deadly effects on many creatures including amphibians, birds, mammals, insects and plants.

Artificial Lights Disrupt the World’s Ecosystems

Nocturnal animals sleep during the day and are active at night. Light pollution radically alters their nighttime environment by turning night into day.

According to research scientist Christopher Kyba, for nocturnal animals,

“the introduction of artificial light probably represents the most drastic change human beings have made to their environment.”

“Predators use light to hunt, and prey species use darkness as cover,” Kyba explains “Near cities, cloudy skies are now hundreds, or even thousands of times brighter than they were 200 years ago. We are only beginning to learn what a drastic effect this has had on nocturnal ecology.”

Chris Kyba

Glare from artificial lights can also impact wetland habitats that are home to amphibians such as frogs and toads, whose nighttime croaking is part of the breeding ritual. Artificial lights disrupt this nocturnal activity, interfering with reproduction and reducing populations.

Artificial Lights Can Lead Baby Sea turtles to their Demise

Sea turtles live in the ocean but hatch at night on the beach. Hatchlings find the sea by detecting the bright horizon over the ocean. Artificial lights draw them away from the ocean. In Florida alone, millions of hatchlings die this way every year.

Artificial Lights have Devastating Effects on Many Bird Species

Photo by Michael Menefee

Birds that migrate or hunt at night navigate by moonlight and starlight. Artificial light can cause them to wander off course and toward the dangerous nighttime landscapes of cities. Every year millions of birds die colliding with needlessly illuminated buildings and towers. Migratory birds depend on cues from properly timed seasonal schedules. Artificial lights can cause them to migrate too early or too late and miss ideal climate conditions for nesting, foraging and other behaviours.

Ecosystems: Everything is Connected

a 15 second exposure showing the behaviour of insects around artificial lights. Image: Nevit Dilman It is dark and there is a streetlight attracting insects to it. Because it is a long exposure you can see the trails the insects make as they travel towards and around the light.
a 15 second exposure showing the behaviour of insects around artificial lights. Image: Nevit Dilman

Many insects are drawn to light, but artificial lights can create a fatal attraction. Declining insect populations negatively impact all species that rely on insects for food or pollination. Some predators exploit this attraction to their advantage, affecting food webs in unanticipated ways.

Energy Waste

Lighting that emits too much light or shines when and where it’s not needed is wasteful. Wasting energy has huge economic and environmental consequences.

In an average year in the U.S. alone, outdoor lighting uses about 120 terawatt-hours of energy, mostly to illuminate streets and parking lots. That’s enough energy to meet New York City’s total electricity needs for two years! We estimate that at least 30 percent of all outdoor lighting in the U.S. alone is wasted, mostly by lights that aren’t shielded. That adds up to £3 billion and the release of 21 million tons of carbon dioxide per year! To offset all that carbon dioxide, we’d have to plant 875 million trees annually.

Environmental responsibility requires energy efficiency and conservation

  • Installing quality outdoor lighting could cut energy use by 60–70 percent, save billions of £££ and cut carbon emissions.
  • Outdoor lighting should be fully shielded and direct light down where it is needed, not shining up into the sky.
  • Unnecessary indoor lighting – particularly in empty office buildings at night – should be turned off.

New lighting technologies can help conserve energy

  • LEDs and compact fluorescents (CFLs) can help reduce energy use and protect the environment, but only warm-white bulbs should be used. Learn more about LEDs and colour temperature from our LED Practical Guide.
  • Dimmers, motion sensors and timers can help to reduce average illumination levels and save even more energy.

Quality lighting design reduces energy use and therefore energy dependence. It also reduces carbon emissions, saves money and allows us to enjoy the night sky. Watch a clip of the documentary The City Dark to learn how lighting design can reduce light pollution and also conserve energy.

Lighting, Crime & Safety

There is no clear scientific evidence that increased outdoor lighting deters crime and in some cases increased outdoor lighting actually increases crime.

A 2015 study published in the Journal of Epidemiology and Community Health found that streetlights don’t prevent accidents or crime, but do cost a lot of money. The researchers looked at data on road traffic collisions and crime in 62 local authorities in England and Wales and found that lighting had no effect, whether authorities had turned them off completely, dimmed them, turned them off at certain hours, or substituted low-power LED lamps.

According to the 2015 study, “[W]hen risks are carefully considered, local authorities can safely reduce street lighting saving both costs and energy … without necessarily impacting negatively upon road traffic collisions and crime.” In fact, most property crime occurs in the light of the day. And some crimes like vandalism and graffiti actually thrive on night lighting.

A 2011 study of London street lighting and crime, showed that there is no good evidence that increased lighting reduces total crime.” A 1997 National Institute of Justice study concluded, “We can have very little confidence that improved lighting prevents crime.”

The truth is bright, glaring outdoor lighting can increase crime and decrease safety by making victims and property easier to see. A Chicago Alley Lighting Project showed a correlation between brightly lit alleyways and increased crime.

Streetlight Glare

Photo by Jim Richardson.

Brighter Does Not Mean Safer:

According to a 2012 AMA report, “Glare from nighttime lighting can create hazards ranging from discomfort to frank visual disability.”

Outdoor lighting is intended to enhance safety and security at night, but too much lighting can actually have the opposite effect. Visibility should always be the goal. Glare from bright, unshielded lights actually decreases safety because it shines into our eyes and constricts our pupils. This can not only be blinding, it also makes it more difficult for our eyes to adjust to low-light conditions.

The Solution? The Right Type of Light Used in the Right Way at The Right Time

Lighting that is the correct type, correct brightness, pointed and switched on only where you need it, is the solution. Why not become a member of the IDA-UK to find out more?

Night Sky Heritage

The nighttime environment is a precious natural resource for all life on Earth, but the glow of uncontrolled outdoor lighting has hidden the stars and changed our perception of the night.

“For my part I know nothing with any certainty, but the sight of the stars makes me dream.”

— Vincent van Gogh

The Natural Night Sky Inspires

Until recently, for all of human history, our ancestors experienced a sky brimming with stars – a night sky that inspired science, religion, philosophy, art and literature, including some of Shakespeare’s most famous sonnets.

The natural night sky is our common and universal heritage, yet it’s rapidly becoming unknown to the newest generations.

Van Gogh painted his famous “Starry Night” in Saint Rémy, France, in 1889. Now, the Milky Way can no longer be seen from there. If he were alive today, would he still be inspired to paint “Starry Night”?

Experiencing the night sky provides perspective, and inspiration, and leads us to reflect on our humanity and place in the universe. The history of scientific discovery and even human curiosity itself is indebted to the natural night sky.

Without the natural night sky we could not have:

  • Navigated the globe
  • Walked on the Moon
  • Learned of our expanding universe
  • Discovered that humans are made of stardust
Some examples of dark sky objects you can see and image in a dark sky site.
Deep sky objects that are visible at a proper dark sky site. Image: A montage by Chris Duffy & Dr Martin Kitching

International Dark-Sky Places Program

For these reasons, IDA established the International Dark Sky Places Program in 2001 to recognise excellent stewardship of the night sky. Designations are based on stringent outdoor lighting standards and innovative community outreach.

Since the program began, more than one hundred Parks, Communities, Reserves, and Sanctuaries have received International Dark Sky Place designations.

Human Health

Exposure to Light Pollution Harms Your Health

Research suggests that light pollution negatively effects human health, increasing risks for obesity, depression, sleep disorders, diabetes, breast cancer and more.

Many species (including humans) need darkness to survive and thrive.

— American Medical Association Council on Science and Public Health (2012)

Circadian Rhythm and Melatonin

Like most life on Earth, humans have a biological clock called your circadian rhythm. It is a sleep-wake pattern governed by the day-night cycle. Artificial light at night disrupts that cycle.

Our bodies produce the hormone melatonin in response to our circadian rhythm. Melatonin helps keep us healthy. It induces sleep, boosts the immune system, lowers cholesterol, and helps the functioning of the thyroid, pancreas, ovaries, testes and adrenal glands. Nighttime exposure to light pollution suppresses melatonin production.

Blue Light is the Most Harmful Type of Light Pollution

Exposure to blue light at night is harmful. Unfortunately, most LEDs used for outdoor lighting — as well as computer screens, TVs, and other electronic displays — have a white colour which is dominated by blues.

According to experts at Harvard Medical School,

“If blue light does have adverse health effects, then environmental concerns, and the quest for energy-efficient lighting, could be at odds with personal health. ”

A 2016 American Medical Association report expressed concern about exposure to blue light from outdoor lighting and recommends shielding all light fixtures and only using lighting with 3000K colour temperature and below.

To minimize harm from blue light in your home, choose the right light bulb and download a colour temperature app that adapts your electronic screen to the time of day – cool light during the day and warm light at night.

Colour Temperature Apps:

  • F.lux is available for Mac OS/X, Windows, Linx and (jailbroken) iPhones and iPads.
  • For those with Apple devices using the iOS 9.3 operating system and above, the Night Shift app is pre-installed. Click here to learn how to use it. 
  • Lux is available for Android devices free or for pay.
  • Twilight is available for smartphones or tablets.

Choosing the Right Bulb


In this picture both lights are “white” but the bulb on the left is rich in blue light, while the one on the right isn’t. The warmer light on the right is the better, healthier one to choose.

All packaging for new light bulbs provides colour temperature information. Use low-colour temperature light sources for interior and exterior light. Their light is less harsh and less harmful to human health and the environment. Look for warm white sources with a colour temperature of 3000K or lower.

Kelvin Temperature Scale

Higher colour temperatures mean white light that is more blue-ish and less warm, the kind that should be avoided after dusk.

3 types of light bulbs showing different effects of colour temperatures.
Image: Wikipedia, shows three different white lights with blue, yellow and orange tints to them. The orange 2700K light is the healthiest and most environmentally positive type to chose.

Glare from Bad Lighting is a Safety Hazard

Glare from poorly shielded outdoor lighting is also harmful to your health because it decreases vision by reducing contrast. This limits our ability to see potential dangers at night. Ageing eyes are especially affected.

“Glare from nighttime lighting can create hazards ranging from discomfort to frank disability.”

American Medical Association Council on Science and Public Health (2012)

Measuring Light Pollution

Jesus Acosta, the impact of light pollution as seen during a power outage.

Due to light pollution, the night sky over many of our cities is hundreds of times brighter than a natural, starlit sky. This skyglow hides the stars from our sight and prevents us and all life on Earth from experiencing a natural night, even in areas hundreds of miles away from towns and cities.

How can you help?

Lincoln cathedral at night
Lincoln Cathedral. Image: Mark McNeill

Become a Citizen Scientist

The CPRE does an annual star count which you can do from your back garden or yard. Anyone can take part in it, and you don’t need specialist training or equipment. Find out more here.

Participating in the Globe at Night citizen-science campaign is a great way to help our understanding of skyglow and its impact. No special tools are required and observations can easily be reported by smartphone, tablet or computer.

It’s also possible to use your smartphone to make night sky brightness measurements. The Dark Sky Meter app makes use of the iPhone camera to record the brightness of the night sky, while the Loss of the Night app walks the user through the sky as measurements are made with a different sensitive tool – the human eye. It’s available for both Android devices and iPhones. And now, thanks to the MySkyatNight project, you can also do your own analysis of all this available data.

Jodrell Bank under a starry sky but with some light pollution showing in the background
Jodrell Bank under a starry but light polluted sky. Image: Mark McNeill

Another way you can help is by participating in the Cities at Night project, which relies on citizen scientists to map and identify photos of cities taken from the International Space Station. This valuable information helps researchers better assess light pollution across of the globe.

In addition to the smartphone apps and the Globe at Night project, more rigorous, long-term monitoring is also being conducted. The section below describes standards for collecting and reporting skyglow measurements.

How Can You Help With Skyglow Observations?

The introduction of the Sky Quality Meter and the International Year of Astronomy Lightmeter have led to a large number of permanent online skyglow monitoring stations. At the same time, a number of individuals and groups have developed their own non-commercial devices for measuring skyglow.

If there is a dark sky park or reserve near you, they are always on the lookout for volunteers to help them with their dark sky measurements.

a before and after picture showing how bad lighting can be improved using IDA guidelines
a before and after picture showing how bad lighting can be improved using DarkSky guidelines. Image: DarkSky