It's our most visible alteration of the planet, easily seen from space: the millions of lights added to our cities due to our fear of the dark. We need them to keep our cities safe. Or do we? A series of studies on crime have revealed that we probably don't need as many city lights as we think — and we might be better off without them.
An excellent piece in Astronomy Magazine by Eric Betz explores what happened when about 100 British cities decided to dim or turn off their streetlights, either to save money on power or to avoid maintenance costs. About a third of the lights are now out in the UK. Surely the streets are running rampant with vice. As it turns out, darker streets didn't mean more dangerous streets.
Betz looks at a study by the University College London (UCL) that crunched 14 years of data in 63 British cities, some of which had gone dark. The researchers examined both vehicular crashes and crimes in places where lights had been switched off:
That research shows less than 1 per cent of all nighttime traffic collisions occurred on streets where the lights had been switched off. And overall, the statistics showed no link between accidents and dimming, reducing, or changing the style of streetlights.
Secondly, the researchers looked at lighting's effect on crime trends. In regions of reduced lighting, they found, there was no increase in burglary, auto theft, robbery, violence, or sexual assault.
While the connection between darkness and crime can't be totally conclusive — crime rates may have naturally been going down anyway — researchers said it was "encouraging" that crime didn't skyrocket just because the streetlights were out.
But that's not how the residents saw it, as another study showed. The London School of Hygiene and Tropical Medicine talked to 520 people from eight cities, some which had their lights switched off. Although many people didn't notice at all, those who knew their neighbourhoods were darker were upset. People reported feeling less safe and thought it showed neglect by city officials.
While many cities are switching to hyper-efficient LED streetlamps to save energy, it turns out this kind of light is especially awful for us and the animals we share our cities with. It's also especially troubling for dark sky advocates who are trying unsuccessfully to get cities to switch to streetlights engineered to preserve residents' starry views. There seem to be plenty of good reasons to dim or turn streetlights off completely, but the perceived fear of darkness might be enough for cities to keep them blaring bright.
Tonight in the US is a nationwide event called National Night Out, where local police hold nighttime events which are meant to gather neighbours and help them to organise community crime watches. People are encouraged to buy glow-in-the-dark wearables, whistles, and flashing lights to keep them visible on dark streets. But if anything, having a special, police-sanctioned night where it's "safe" to go out after dark reinforces the idea that night is dangerous and that neighbours shouldn't really be out the rest of the time when the sun goes down. It proves how hard the battle will be to win for scientists and environmentalists who want to take back the night.