Years ago, a student out for a night run at a nearby university campus was grabbed by an assailant. She managed to get away physically unharmed, but the sense of safety in the wealthy suburban community was not so lucky. The student had been running on a sidewalk through a remote area of campus surrounded by athletic fields and woods. There was an immediate call for better lighting since the crime occurred in an area where the only lighting was from widely spaced streetlamps. As a sign of the university administration’s responsiveness, additional lighting construction began within days.
Security lighting is a first choice for nighttime crime prevention. But how effective is it and how much is enough? Without answers to these questions, each criminal incident causes a knee-jerk reaction to add a light here and a light there. Eventually, every place a person might wander after dark becomes bathed in continuous light. So, what is the appropriate level? The surprising answer may be almost none at all.
Monuments to fear
We are so reliant on vision, our widest-ranging sense, that to be robbed of it, even momentarily, can create an almost paralyzing sense of vulnerability and apprehension. Fear of the dark (and the things lurking within it) is so universal that it seems innate — perhaps an evolutionary adaptation to nocturnal predators. Historian A. Roger Ekirch delves into a history of human activities at night in his 2005 book At Day’s Close. Be it wild animals, malevolent humans, supernatural miscreants, or unseen falls, fear of nighttime danger has been widespread throughout history and across cultures — even the mighty Zeus feared Nyx, the ancient Greek goddess of night. It is no surprise that control of fire is considered such a major technological advance for early humans. In its many forms — torches, candles, lanterns, etc. — early artificial night illumination helped alleviate nocturnal anxieties and expand the time and range of human activity.
Today, the fear of wild animals and the supernatural are greatly reduced, but the fear of human criminality and violence remains. Meanwhile, our need for safe nighttime transportation has only increased. So, let us explore the actual safety benefits of night lighting.
A 2008 review of 13 prior US and British studies on the use of street lighting to prevent crime was mixed. Overall, the studies found that additional lighting decreased crime on average 20%, but this effect only held in communities where both day and night crimes were included. The studies that measured only nighttime crime showed no significant improvement. Meanwhile, the studies that measured both day and night crime had no relative decrease in the night crime rate compared to the day crime rate. This suggests that any improvement came not from the lighting itself, but from some other factor not measured in the studies. The authors proposed the improvements were due to community pride rather than actual deterrence, yet this research has still been used to advocate for more crime deterrence lighting.
The one thing that most experts agree on is that outdoor night lighting reduces the fear of crime. However, a 2013 review of interventions to reduce fear of crime (not actual crime rates) found that 16 studies to improve street lighting showed mixed results — only 11 studies showed a reduction in public fear and the more rigorous studies were the least conclusive. Nonetheless, the evidence for night lighting reducing the fear of crime is stronger than the evidence for it reducing actual crime.
Teasing out the effects of night lighting on crime requires creativity. Practical and ethical controlled experiments are difficult to perform and clever methodology is needed to remove other explanations. One interesting study compared the difference in crime rates between nights with full moons and moonless nights. While moonlight is much dimmer than sunlight, it is only about 100 times dimmer than typical office lighting and still an order of magnitude brighter than the lower limits of human vision. For this reason, farmers and travelers of centuries past revered the full moon for its ability to light the way at night. Perhaps that is the reason that the 2016 study of the impact of moonlight on criminality found an increase in outdoor crime as moonlight increased. The researchers proposed that a full moon provided just enough illumination for criminals to be active but without the telltale signs of criminal activity that a flashlight might give away. It is also possible that the additional light reduced public fear of crime and encouraged more people out at night thereby increasing their risk of victimization.
In the absence of conclusive evidence, we often turn to anecdotal evidence. In his book on light pollution, astronomer Bob Mizon notes a few unintended tests of crime lighting. For example, a multi-week power blackout in Auckland, New Zealand in 1998 caused crime levels to fall rather than increase. This would support the plausible argument that darkness deters crime because criminals can’t see in the dark any better than victims — hence the reason why most crime occurs during the day.
Ultimately, given the difficulty of measuring the crime deterrence of night lighting, it is likely that any benefits are small and specific if they exist at all.
The other known benefit of night lighting is transportation safety. Here the benefits are a bit more obvious — the likelihood of injury from walking on a lit sidewalk is clearly lower than stumbling around in total darkness. Instead, the question centers on the appropriate use of light. Vehicles are equipped with headlights and every smartphone has a flashlight. So how much additional lighting is needed?
A 2006 study detailed some statistics on the higher rates of severe injuries from night driving compared to daytime driving. While the higher injury rates at night have multiple causes including fatigue and alcohol use, lower visibility would appear to be an important factor because accident rates are lower on streets with lighting. However, the study also compared unlit night driving injury rates between the UK and Greece and found the latter to have a rate five time higher. Considering that night is a universal phenomenon, this would suggest that other engineering or behavioral differences are also important.
A more recent study used traffic collision data from 2000 to 2013 in England and Wales to assess the impact on changing street lighting. The study found no statistically significant change in nighttime accident rates for roads where the streetlights had been dimmed, turned off for part of the night, or even turned off entirely. This contradicts the results of a 2009 systematic review of 17 controlled before-after studies in the US, UK, Germany, and Australia which suggest that there is a meaningful decrease in crashes and fatalities when street lighting is installed.
Regarding pedestrians and cyclists, there is a consensus that street lighting reduces the rate of nighttime accidents. However, the degree of benefit is unclear. For example, one study in the Czech Republic estimated that street lights cut night bicyclist fatalities in half, while a study in Montreal found higher bicycle and pedestrian accident rates in areas with better lighting. The authors of the counterintuitive study proposed that either lighting was being added to areas with otherwise higher accident rates or that motorists drove more cautiously in areas with poor lighting. Either way, more lighting may not be the solution for all night transportation safety issues.
This is especially true if the lighting is poorly designed. Lighting that creates areas of glare and shadow actually decreases transportation safety. In these cases, nighttime pedestrians and cyclists would be safer with less street lighting — particularly if it required them to carry a light source that would have the secondary benefit of making them more visible to vehicles.
The general takeaway from these studies is that there appears to be traffic safety benefits from outdoor lighting, but they are more complicated and less robust than the public assumes. Additionally, as safety features, such as automated emergency braking, become standard features on all vehicles, the safety benefits of night lighting will further diminish.
Having reviewed the uncertain benefits of night lighting, let us summarize the known costs.
Despite the rapid adoption of energy-efficient LED lighting, outdoor lighting in the US still consumes about 380 billion kWh of energy annually at a cost of $10 billion. That is a lot of carbon emissions. Even if some of the energy is obtained from renewable sources, night lighting displaces other essential energy-consuming activities that could use the renewable energy. Likewise, the operating cost statistics don’t consider the additional energy, material, and labor costs of manufacturing, installation, and maintenance. In short, outdoor lighting is expensive.
Aristotle’s History of Animals, written over two millennia ago, mentions the attraction of some animals to night lighting, but scientists have only more recently explored the impacts of artificial night lighting on ecosystems. The 2006 Ecological Consequences of Artificial Night Lighting, edited by Catherine Rich and Travis Longcore, was the first effort to bring together the research of a range of experts on the mostly negative effects of artificial night lighting on a variety of mammals, birds, reptile, amphibians, fish, insects, and even plants. Continuing research suggests that the collective ecological impacts of night lighting are substantial. While recent news of accelerating biodiversity loss is blamed primarily on habitat loss and climate change, it would seem wise to minimize additional stressors on the ecosystem.
Insects, in particular, are known to be very sensitive to night lighting and are undergoing such declines that some have called it an “insect apocalypse.” While data may indicate declines primarily due to modern pesticides, anything that can minimize unnecessary harm is desirable given that insects not only provide essential pollination services, but also serve as a critical link in the food web and dispose of dead organisms and waste. Fireflies are particularly threatened by light pollution because it disrupts their mating rituals. Momentarily ignoring their ecological function, to lose these charming summer visitors would be sad indeed.
There is a variety of research regarding the value of sleep — although the amount of sleep needed and ideal patterns of sleep are still in question. Since the explosion in smartphone use, the impact of excessive screen time on natural sleep cycles has been a popular topic. However, there is substantial evidence that negative sleep impacts are triggered by most forms of artificial night lighting. Negative health impacts may also extend beyond fatigue to a host of other concerns ranging from breast cancer to obesity. The theory is that light exposure at night reduces the production of melatonin, a hormone that slows body functions such as cell division (including cancer cells), lowers blood pressure, and promotes the production of immune cells. While it’s most relevant to indoor lighting because that is where industrialized societies spend most of their time, it’s worth noting that the health impacts apply to outdoor lighting as well. Even a streetlight shining through a bedroom window can measurably curb melatonin levels.
Furthermore, modern society’s willingness to trade sleep for productivity with night lighting has substantial health costs. The affordability of artificial lighting has extended our work and play far beyond the confines of the natural day. Factories running around the clock are viewed as a sign of prosperity. Road construction is now done at night to prevent slowing the daytime flow of commerce and commuters. It seems a bit old-fashioned to suggest that darkness gives us respite from toils traditionally performed in full daylight. However, the importance of maintaining natural darkness may eventually become a standard component of public health policy and we may realize that a daily biological pause in activity is something more than a loss of productivity or a nuisance.
The big break for science fiction luminary Isaac Asimov came with “Nightfall,” published in 1941. The short story describes a civilization on a planet with multiple suns that never experiences night. When a total solar eclipse that occurs once every two millennia is upon them, scientists expect that the prolonged darkness will cause mass hysteria, but they fail to anticipate the true vastness of space that is revealed to them when they see a sky full of stars for the first time. The story was inspired by a passage from Ralph Waldo Emerson asking what would happen “if the stars should appear one night in a thousand years.” Asimov grew up in New York City, so it was perhaps easier for him to imagine a life without stars.
Most of the world’s population now experiences a degraded view of the stars due to light-polluted skies. Given that light pollution has been slowly increasing for decades, it is likely most people do not notice what is happening or realize that we should be able to see thousands of stars on a clear night instead of hundreds (or tens if you live near a major city). If you are interested in seeing the changes in nighttime lighting where you live, Radiance Light Trends, a website developed by Christopher Kyba of the GFZ German Research Centre for Geosciences simplifies the analysis of satellite light emissions data.
Past initiatives to reduce unnecessary street lighting have met with mixed, but limited public reaction. Some individuals complain of public safety concerns and a loss of modernity, while others praise the energy reductions and improved night sky views, but reductions in street lighting go unnoticed by most residents. It seems we have forgotten about the night.
The price of modern society’s gradual disassociation from night has been a subject of exploration by Paul Bogard — first in a 2008 edited collection of essays, Let There be Night, and then in the 2013 book, The End of Night. Professor Bogard focuses on the unquantifiable aesthetic, philosophical, and even spiritual value of darkness. The diminution of night is not merely a matter of energy or ecological loss — it is also a loss of culture, beauty, and awe.
Yet, whether the cause is a sullied view or modern distractions, the stars seem to have lost their attraction. A few recent attempts at space art have inadvertently demonstrated that most of society no longer watches the night sky. In early 2018, a 1-meter diameter geodesic sphere, named Humanity Star, was launched from New Zealand by a private aerospace company. The giant disco ball, visible to the naked eye, orbited every 90 minutes for two months before burning up as it prematurely fell out of orbit. Unless you are an amateur or professional astronomer, you probably never heard of this feat which, depending on who you asked, was a celestial art installation, publicity stunt, or space junk. Nor did you likely hear about the similar failed Mayak or Orbital Reflector projects either.
This seems to indicate that space art — or worse, space advertisement — is a bad idea. The primary audience for space art lives in industrialized urban areas with extreme light pollution and is not in the habit of viewing or appreciating the night sky. Conversely, people who have access to an unpolluted night sky tend to like it that way. The most reliable audience is amateur and professional astronomers — a group generally hostile to the idea of glittery space junk without function. Thus, the total appreciative audience for space art or advertisement is very small compared to the cost of installation.
One can hope that this is not the start of a new fad. If so, an international agreement to ban heavenly self-promotion and other presumptuous intrusions into the night sky may be necessary. However, given the recent rise of megaconstellation satellites, professional astronomers may have bigger problems than a few pieces of space art.
People do not give up something perceived to have essential benefits. However, if the crime and transportation safety benefits of artificial outdoor night lighting have been greatly overestimated, then effecting a public policy change becomes possible — especially if people are reminded of the value of darkness. The good news is that research suggests that most people are amenable to reducing light pollution when made aware of the benefits of reduced night lighting. The other piece of good news about light pollution is that it is one of few forms of pollution that doesn’t require much effort to remove. While some of its negative ecological impacts may take a while to recover, other effects end as soon as we turn off the unnecessary lighting.
Of course, the problem is not so easily solved. Recent maps of global nighttime illumination give an idea of the spatial scope of the problem. Likewise, geographer Matthew Gandy uses the term “negative luminescence” to encompass light pollution’s myriad harmful impacts to ecosystems, energy use, human health, and aesthetics that are enmeshed in the technology and culture of modern society. Retaining the positive qualities of artificial night lighting while separating and discarding the negative effects requires effort.
Many of the efforts to educate the public have been led by the International Dark Sky Association. However, an increasing number of popular press pieces are needed to educate the public followed by informed action, both personal and public policy. Outdoor LED lighting is more efficient and environmentally friendly than alternatives, so switching over from incandescent, halogen, and fluorescent bulbs to LEDs is wise and necessary. However, the efficiency of LEDs makes them a little too easy to abuse. Consumers can now buy cheap solar-powered outdoor LEDs that can be installed with little effort. Decorative driveway lights are popping up everywhere like little glowing mushroom after a rain.
Rather than follow the latest lighting industry fad, here are some sensible guidelines.
1. Night lighting should be used in high traffic areas for pedestrian and vehicle safety only — avoid lighting for decoration, architectural accents, crime prevention, and other dubious applications.
2. Lights should only point downwards and have adequate shielding. Lights pointing sideways cause light trespass and create unsafe glare. Any light pointing or reflecting upwards contributes to skyglow — the diffuse scattered light over every urban area that signals wasted energy. Unless you’re operating an airport, use shielded lights that point only at the path or road where it’s needed.
3. Use motion sensors. They reduce light pollution, saves energy, and provides better crime deterrence. However, be careful not to put security lighting in secluded locations where no one is likely to see the crime — the “security” lighting merely becomes courtesy lighting for criminals. Motion sensors are now also widely available for street lighting and can be integrated with automatic controls that also reduce brightness during the middle of the night — the reduction in energy use and light pollution is substantial.
4. Brighter lights provide better color distinction, but often decrease safety because they create more low-visibility areas of glare and shadow. It’s usually better to have two dim lights than one bright one.
5. To minimize negative health and ecological effects of night lighting, choose lighting that mimics firelight or sunsets rather than lighting that mimics bright daylight. LED lighting is usually labeled with its correlated color temperature (CCT). A CCT of less than 3000K is considered a “warm” light while over about 5000K is a “daylight” source. Outdoor lighting should have a CCT of 3000K or less. The appropriate use of “daylight” lighting at night is limited — surgical operating rooms would be a good example. Outdoor stadium lighting is not.
Asking if an outdoor light is needed at all should always be the first question. If the light fixture isn’t there, there will be no installation cost, no operating costs, and no maintenance costs. The most beneficial locations for outdoor night lighting are where there are many nighttime pedestrians and vehicles, such as city streets. In these cases, the lighting serves two purposes backed by research — pedestrian and driver safety.
Installing a single outdoor light fixture seems like an unimportant decision, but the accumulation of many small decisions can have large consequences. Collectively, it’s as if modern civilization is still trying to allay its deep-seated fear of the dark with a proliferation of night lights, yet we now know that being continuously bathed in light is unhealthy and some darkness is necessary and beautiful.
Astronomer Christian Luginbuhl has noted that light pollution is not an unsolvable problem, but it requires us to stop pigeonholing light pollution as an issue only for astronomers. If you look up at the night sky and can’t see the Milky Way, you are affected by light pollution. While we often extol the value of traveling to see the world, a good dark night will let you see the universe. It’s hard to put a price tag on that kind of perspective.