Most of us have probably experienced a fear of the dark. Some evolutionary biologists have linked this fear to the fear of predators from a time when humans were not on top of the food chain. And this innate anxiety, difficult to quantify with numbers, probably plays a part in the lack of public will to get rid of street lighting.
"You have to take into account the views of the communities," said Edwards. Without the support of the public, changes are simply not possible. Because ultimately, scientists don't plan cities -- government officials, often elected by the people, do.
"In the U.K., there are people who are very vocal about this, and they would say things like 'How dare you turn the lights out? We're paying our [taxes]!' There was even an opposition [when a local township was planning on reducing street lighting] where the community got together and said 'Look, we'll pay more -- how much more do we need to pay to keep our lights on?'" said Edwards.
While people may struggle to change their preferences about street lighting in their local neighborhood, there are other sources of light pollution, such as those along highways and in industrial and commercial buildings, that may be easier to curtail.
Blinded by the lights
In 2012, the Federal Highway Administration, under the U.S. Department of Transportation, published an update to the 1978 handbook for road lighting design. The update included considerations for the negative impact of excessive lighting, while the older approach mainly focused on recommending the minimal lighting requirements -- for example, the minimum lighting needed for a stretch of road leading up to an intersection, given the speed limit and the curvature of the road.
So, what does the data say about the correlation between accidents and streetlamps on highways?
In 1992, the International Commission on Illumination, a nonprofit organization headquartered in Vienna, Austria, published a report that examined 62 studies of lighting and road accidents from 15 countries. While 85% of the studies claimed their data showed lighting to be beneficial in preventing nighttime accidents, only about one-third showed statistical significance. Among that one-third, the reported accident reduction ranged widely, from 13 percent to as much as 75 percent.
How is this huge discrepancy possible? Can't one just set up an experiment with two identical roads, one with light and one without, and compare the numbers?
In addition to logistical difficulties and ethical concerns for such an experiment, the light versus no-light way of thinking is perhaps itself a false dichotomy, since the efficacy of street lighting depends on how the lights are set up.
"Here's an example: Say you're driving on the highway at night, and someone behind you turns on their brights. It flashes on your rearview mirror and you get temporarily blinded," said Mendoza. “The intention is to have appropriate lighting, and that we are not discussing or arguing for removal of all lighting."
There are instances where reduced lighting can actually improve its intended functionality.
"Sometimes you have a bright streetlight, and then 30 meters down the road is another one, but there is kind of a 'light trough' in between where it is much darker and your eyes can't see," he said. "If we dimmed these lights, these troughs would appear less deep, and your eyes can see better."
There are also other sources of light besides streetlamps lining our roads, some of which probably do more harm than good when it comes to preventing accidents.
"One of the biggest hazards is electronic billboards, as they are sparsely regulated, if at all. Some of them don't even have a night mode, meaning they are as bright at night as they are during the day when they are competing with the sun," said Mendoza. These billboards can be especially dangerous, say, when they display a blindingly white advertisement right after one with a darker color scheme. "They are a huge distraction that could be really dangerous."
Sleepless bright nights
Speaking of distractions, lighting at night can also affect sleep and human health.
While people may be most aware of the effects of looking at smartphones and TV screens at night, outdoor lighting can also invade people's bedrooms. Growing up, I remember being able to read my comic books using the streetlight shining through my bedroom window, long after my mom had turned out the light and told me to go to bed.
Researchers have noticed the effect this modern way of living may have on our bodies, most notably through the disruption of our circadian rhythm.
"Although it is difficult to prove whether artificial light can harm you directly -- it's not as straightforward as something like smoking, for example -- what it does is it alters your circadian rhythm, which can lead to a wide range of health problems," said Mendoza.
For one thing, people with disrupted circadian rhythms often don't get enough sleep. In 2014, the U.S. Centers for Disease Control and Prevention declared sleep deprivation to be a "public health epidemic," and some researchers consider it to be a rising global epidemic. Lack of sleep has been linked to a variety of health problems, ranging from relatively unsurprising ones such as depression to certain forms of cancer and even Alzheimer's.