Looking up at the thousands of street lights that illuminate our cities, former town planner and designer Danny Bettay has always asked one simple question: "Do we really need this, or is this overkill?".

"Historically, street lights were designed, indirectly for people, but designed for technologies, essentially for horse and carriage,"  Mr Bettay said.

"And over 200 years of having these infrastructures embedded in our environment, we have slowly come to realise that there's some environmental harms of technologies that we've created in the past."

In order to reduce the impact street lighting has on the environment, Mr Bettay initiated a trial in Canberra of something called "adaptive lighting"  — dimming or brightening street lights to match people's needs at the time.

Of Canberra's roughly 83,000 streetlights, more than 30,000 have been fitted with LED globes and "smart nodes",  which allow their brightness to be controlled remotely from a laptop.

So between 11pm and 5am during the first half of 2024, the streetlights, mainly in areas less used at night, were dimmed 10 per cent every 15 minutes until they were at half of their usual brightness.

Clearing the sky

Up at Canberra's Mt Stromlo Observatory, astronomer Brad Tucker was monitoring cameras measuring how bright the night sky was, and along with satellite data, looking to see whether the dimming was revealing more of the night sky.

"So what we were finding during this dimming is that as the lights would dim, we could definitively ... measure a reduction of light pollution," Dr Tucker said.

"So when we dim all the way to about 50 per cent, that means the sky has been reduced by about 25 per cent in terms of brightness."

Adjust these suburban lights and see how they change the night sky (notes)

Dr Tucker said with even a 25 per cent clearer view of the night sky, the amount of extra detail was profound.

"So as that gets to that 25 per cent level, we're seeing 25 per cent 'darker-ness' of the sky, so we'll see more stars," Dr Tucker said.

"We'll see the fainter stars will be a bit brighter, the brighter stars will get even brighter, and some new stars pop out that were previously lost.

"Things like the Milky Way, detail of the Milky Way got a little bit more better resolved as that sky dropped."

On top of the reduction in light pollution, the scientists found the reduction in brightness of the lights reduced their carbon emissions by 1,085 tonnes.

The scientists also hope a reduction in light can also help animals who've been disrupted by growing cities and towns.

'Scalable in any context'

The Australian-first trial was started when Mr Bettay was working for private company Omexom, which is contracted by the ACT government and is now the focus of Mr Bettay's PhD at the Australian National University.

Mr Bettay said he hopes the results of their trial can be applied in other jurisdictions, but that the ACT was uniquely placed to embark on the project as its government owns the street-lighting infrastructure, which is not the case in other major cities in Australia.

He's already in discussions with the New Zealand cities of Auckland and Christchurch about the results.

"Auckland is a much bigger city than Canberra, but they have 110,000 lights that are equipped with smart nodes that have been equipped for a while, they just haven't used them.

"They're a city much more akin to Sydney as opposed to Canberra, so they have a night-time economy that they need to take into consideration, so it's a little bit different to Canberra."

Mr Bettay said part of the trial involves monitoring the risk to safety, crime and traffic by reducing light on streets, but that the reduction is often hard for the human eye to detect.

"We've had engineers and other street lighting practitioners who've had 30 plus years experience, who sat out and looked at street lights with us, and they were unable to distinguish between 70 per cent and 100 per cent," Mr Bettay said.

Regaining connection

Dr Tucker hopes reducing light pollution through things like adaptive lighting can help build back our connection to the night sky.

"Humans have been around on this earth for hundreds of thousands of years, but we've kind of erased our connection to the sky in about 100 years," Dr Tucker said.

"We've kind of erased a part of human culture and human history, not just for people like Aboriginal and Torres Strait Islanders with their deep connection to land and sky, but for all of us who, we like to go out and enjoy the views, we like to enjoy out and see what's above.

Interactive notes and credits: The interactive is based on the Bortle scale, as well as results from Dr Tucker's experiments in Canberra. The lighting change interactive is based on a hypothetical suburban area with a Bortle scale level of 7 with light pollution sources: street lights (50 per cent); house lights (40 per cent); sport lights (10 per cent). Solutions to light pollution: changing street lights to LED (50 per cent reduction in light pollution from that source); dimming street lights to 70 per cent (15 per cent reduction); changing sport lights from cool to warm LEDs (15 per cent reduction); shielding outside lights (50 per cent reduction). 

Concept and production: Kylie Andrews; Development: Andrew Hystek-Dunk, Matthew Heffernan; Production: Chloe Brice; Expert advice: Dr Brad Tucker. Return to lighting change interactive