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.

Summary

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).

References

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 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.

https://www.friendsofthelakedistrict.org.uk/News/the-big-switch-off-be-star-struck

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

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]
Wikipedia

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

The night isn’t just for us, it’s essential for life itself. From bats hunting in the twilight to birds navigating by starlight, countless species depend on natural darkness to survive. But when artificial light spills into the night, it throws nature out of balance. What feels like a small glow in our garden, street, or town can have far-reaching consequences for the entire web of life.

The Problem

For billions of years, life on Earth has evolved under the natural rhythm of day and night. This cycle is written into the DNA of every plant and animal. But by lighting up the night, humans have radically disrupted this balance.

“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 darkness to guide essential behaviours — from feeding and migration to reproduction and protection from predators. Increasing scientific evidence shows that artificial light at night is harming, and in some cases killing, countless species: amphibians, birds, mammals, insects, and even plants.

Artificial Lights Disrupt the World’s Ecosystems

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

Research scientist Christopher Kyba notes:
“the introduction of artificial light probably represents the most drastic change human beings have made to their environment.”

Predators rely on light to hunt, while prey species depend on darkness for protection. Near cities, cloudy skies can now be hundreds or even thousands of times brighter than 200 years ago, with devastating consequences for nocturnal ecology.

Amphibians such as frogs and toads, whose nighttime croaking is vital for breeding, are silenced by glare from artificial lights, disrupting reproduction and shrinking populations.

Artificial Lights Lead Baby Sea Turtles to Their Demise

Sea turtles hatch at night on beaches, guided to the ocean by the bright horizon over the water. Artificial lights confuse them, drawing hatchlings inland where millions die every year in places like Florida.

Artificial Lights Devastate Bird Species

Migratory birds navigate by moonlight and starlight. Artificial lights lure them into cities, where countless collide with illuminated buildings and towers. Lights also disrupt seasonal cues, forcing birds to migrate too early or too late, throwing off nesting, foraging, and survival.

Ecosystems: Everything Is Connected

Artificial light creates a fatal attraction for insects, drawing them into harm’s way and reducing populations. This collapse ripples outward: fewer pollinators for plants, fewer insects for birds and bats, and food chains thrown off balance.

There’s Still Hope for Our Wildlife

The damage may sound overwhelming, but the good news is that light pollution is different from other threats, it’s instantly reversible. Every time we shield a light, point it downwards, or switch it off when it’s not needed, we give wildlife back the darkness they depend on to survive.

When communities choose smarter lighting, animal behaviours recover almost immediately. Frogs sing again, birds stay on course, and insects can thrive. By protecting the night, we protect entire ecosystems.

Start at home – take simple steps tonight to reduce light pollution and help wildlife reclaim the night.

Climate Change

Wasted Light, Wasted Energy

When we light up the night sky, we’re also burning through energy, and most of it is wasted. Poorly designed, overly bright, and unshielded lights spill light into the sky instead of focusing it where it’s needed. That wasted energy translates into unnecessary carbon emissions that fuel climate change.

Light Pollution’s Carbon Footprint

Artificial light at night consumes vast amounts of electricity. In many regions, that electricity still comes from burning fossil fuels. The result: more greenhouse gases in the atmosphere and more pressure on our already fragile climate.

Outdoor lighting that’s left on all night when no one is around to benefit adds up quickly. Multiply this by millions of homes, businesses, and cities worldwide, and the impact is staggering.

There’s Hope for a Brighter (and Darker) Future

The good news is that reducing light pollution helps fight climate change directly. Every time we switch off unnecessary lights, use motion sensors, or install energy-efficient, shielded fixtures, we cut energy use and carbon emissions.

A night sky full of stars is not only beautiful – it’s a sign of a healthier planet.

Start at home – make small changes to your outdoor lighting today to protect the climate.

Lighting, Crime & Safety

Bad Lighting Creates Unsafe Environments

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

As of 2025, research shows that dimming or reducing street lighting has not led to an increase in crime. If brighter lights truly prevented crime, then Las Vegas, one of the brightest cities on Earth, would be the safest place in the world.

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.

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.

Safer Streets Through Smarter Lighting

The solution isn’t more light, it’s better light. Shielded, well-placed, warm-toned lighting reduces glare, improves visibility, and creates genuinely safer neighborhoods. Smarter lighting protects people, supports healthier communities, and helps restore the night sky.

Start at home – see how you can improve safety and reduce light pollution with simple changes.

Night Sky Heritage

Losing Our Shared Sky

For most of human history, the night sky was a source of wonder, guidance, and inspiration. Today, light pollution hides the stars from nearly 80% of people worldwide. Entire generations are growing up without ever seeing the Milky Way.

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

A Vanishing Connection

The night sky has shaped our cultures, mythologies, and scientific discoveries. From ancient navigators charting their course to artists and philosophers seeking meaning, the stars have always been part of our shared heritage. When artificial light erases the stars, we lose not only a view, we lose a connection to history, to science, and to each other.

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

— Vincent van Gogh

Restoring the connection to our night sky

The stars aren’t gone – they’re waiting. Communities around the world are reclaiming their skies through dark-sky parks, preserves, and improved lighting practices. With simple changes, we can bring the stars back into view, allowing future generations to experience the same awe that has inspired humanity for millennia.

Start at home – explore small steps you can take to protect your view of the night sky.

Human Health

Exposure to Light Pollution Harms Your Health

Artificial light at night doesn’t just block out the stars, it harms us too. Research shows that light pollution increases risks for obesity, depression, sleep disorders, diabetes, breast cancer, and more. As the American Medical Association noted:

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

How Light Pollution Disrupts Our Bodies

Circadian Rhythm and Melatonin
Our bodies follow a natural sleep-wake cycle called the circadian rhythm. Darkness triggers the production of melatonin, a hormone that induces sleep, strengthens the immune system, and supports vital organs. Artificial light at night suppresses melatonin, leaving us more vulnerable to illness.

Blue Light Is the Most Harmful
Blue-rich light, from LED streetlights, TVs, phones, and laptops is especially disruptive. It brightens the night sky more than other colours and interferes with sleep and health. Even energy-efficient lighting, if too blue, comes at a hidden cost to human wellbeing.

Glare Is a Safety Hazard
Poorly shielded lighting doesn’t just waste energy; it creates glare that reduces vision and contrast, making it harder to see at night. This puts everyone at risk, especially older adults.

There’s Hope for Healthier Nights

Unlike other pollutants, light pollution is reversible. By choosing warmer light sources (2700K–3000K or lower), shielding outdoor fixtures, and using apps that reduce screen brightness and blue light at night, you can protect your sleep, your health, and your loved ones.

Every time we bring back a little darkness, we bring back balance to our bodies.

Start at home – take simple steps today to make your nights healthier.

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.

Category Archives: Light Pollution