Two scientists mapping New Zealand’s light pollution have found our nights became a lot brighter over the past decade—and that most of our public lighting is now bright blue-white light-emitting diodes (LEDs) which negatively affect human and animal health.

Te Pūkenga Nelson Marlborough Institute of Technology ecologist Ellen Cieraad and wildlife biologist Bridgette Farnworth used satellite data to map New Zealand’s light pollution and found it grew by 37.4 per cent from 2012 to 2021. That’s faster than the global average.

Using the Official Information Act, they also found most councils used millions of dollars of Waka Kotahi funding to replace streetlights with LEDs—but at least 77 per cent of those are cool, blue-white LEDs with a colour temperature of 4000 kelvin (K), shown to affect human circadian rhythms and wildlife.

In a paper recently published in the New Zealand Journal of Zoology, bat scientists experimented with 4000K LED floodlights illuminating trees at a Tamahere home, discovering that local critically endangered long-tailed bats avoided the area when lit. That’s contrary to a popular theory that night-time light attracts insects, which attract bats.

In humans, circadian rhythm disruption has been implicated in cancer, obesity, diabetes, depression and sleep disorders, and possibly increases the risk for dementia.

The International Dark Sky Association recommends lights should be 3000K or less; some European countries don’t allow anything over this. A few councils in New Zealand are light-savvy, too. Kaikōura, for example, recently installed dimmable 3000K and 2200K LEDs to help protect the light-sensitive Hutton’s shearwater, which kept crash-landing in town.

But the default was 4000K, says Cieraad. If councils wanted a different temperature of outdoor lighting, they faced extra difficulties to obtain it. “So most councils didn’t.”

It’s bad news for dark-sky scientists and enthusiasts, who long ago realised the plethora of cheap LEDs is threatening the natural night already lost in so many places around the world. A petition to legislate against light pollution, spearheaded by University of Canterbury emeritus astronomy professor John Hearnshaw, is now before a select committee.

But most councils have now spent more than $150 million installing lights that interrupt our circadian rhythms and dazzle wildlife—lights that are too much like daylight for the night under which we evolved. They will be in place for some time. It’s frustrating, but Cieraad is optimistic. Public lighting makes up only about a fifth of light pollution, so there is space for businesses and citizens to be more thoughtful. We can buy less intense lights, or use dimmer switches and motion sensors, or shields that direct light downwards. Or, of course, the off switch.