Science can inform better lighting decisions

The Aurora Australis visible from Dunedin. The right street lighting is vital to make the city...
The Aurora Australis visible from Dunedin. The right street lighting is vital to make the city night-sky friendly, the writer argues. Photo: Stephen Voss.
Lighting Dunedin smartly will benefit everyone, writes Kyra Xavia.

Dunedin has an opportunity to become the first Night Sky City in the southern hemisphere,  but the success of this visionary endeavour hinges upon one important factor: night sky-friendly streetlights. Unfortunately, there’s confusion about what’s involved.

Lighting is a  complex issue.  White LEDs are  being heavily promoted for their energy efficiency, they have other costs, which outweigh energy, maintenance and operational savings. The implications are serious  because LED technology is rapidly being installed around the world.

White LEDs have broader, long-term losses (caused by the disruptive blue and green wavelengths of light they emit), which include harming the health of human residents, endangering wildlife, and degrading what remains of our night sky, an as yet, untapped asset of immense worth to tourism and our community.

While there’s plenty of scientific evidence about the risks of blue-rich light at night, much public outcry against white LEDs (too bright, harsh, and clinical) and a resulting shift towards warmer light, decision-makers are not yet paying enough attention to, or even aware of a critical factor called scotopic/phototopic (S/P) ratio.

This figure measures how much light emitted from a light fixture is useful to the human eye, and most importantly, for a Night Sky City, how much light pollution is generated. For environmental and ecological impact, the S/P ratio, just like the colour spectrum is crucial — unlike the correlated colour temperature (CCT) of an LED, which only indicates the perceived visual warmth or coolness of light in Kelvin (K).

While both the American Medical Association and the International Dark Skies Association acknowledge the risks of exposure to blue-rich light, neither has yet stated that all white LEDs are problematic. In fact, both still recommend a maximum of 3000K, further confusing municipalities  that wish to attain dark sky status.

The New Zealand Transport Agency (NZTA), which sets guidelines for road lighting and design, and co-funds the changeover, has also not yet acknowledged the full range of risks. Nor has Auckland Transport, which has bulk purchasing power and is currently rolling out white LEDs.

As Dunedin city councillors have committed to the Urban Design Protocol, which covers custodianship of the environment and people under its care, they have a responsibility to illuminate Dunedin safely and well. To honour this commitment, new streetlights must not exceed the level of blue and green wavelengths of current streetlights, and they must also have a similar or improved S/P ratio of 0.4 to 0.6.

Sadly, warm white LEDs (2700-3000K) breach both — even when shielded and at the same lumen output as the lights they replace. In fact, with an S/P ratio of 1.3, these LEDs will worsen existing light pollution, doubling what we have now and impacting on areas up to 100km away.

We know artificial light at night (ALAN) has negative consequences on wildlife as it impairs biological processes required for health in every species with a dark/light cycle, disrupting too, communication habits, foraging, mating and orientation.

Exposure to blue-rich light also suppresses the production of melatonin (a powerful antioxidant with protective immune, anti-inflammatory, and tumour suppressing activity). For humans, this means an increased risk of Alzheimer’s, cancer, diabetes, depression, obesity and other diseases.

Although people can reduce their exposure to blue-rich light in their own homes, it’s impossible to do so outdoors with white LED street lights. Nor can wildlife and ecosystems escape.

Blue wavelengths of light also scatter in the eye to create a "veiling" effect, resulting in visual discomfort, dangerous disability glare, and noticeably more contrast, which further diminishes night-time vision. (White blue-rich light is perceived as being 3-5 times more glary than orange light — as seen with the blinding headlights on modern cars.) For young people, mature drivers (a large percentage of the population), and those with impaired vision, white LEDs pose an even greater risk. Claims that white blue-rich LEDs improve traffic/pedestrian safety and reduce criminal activity remain unfounded and some recent research contradicts this assumption.

Not only that, the intense light from white LEDs causes the pupil to contract, so while the sky appears darker, the human eye is unable to detect all but the brightest stars. All of which makes white LEDs unsuitable for a Night Sky City. Orange street lighting has been safely used for  more than 60 years, and its colour rendition has not been an issue (until the lighting industry’s strong push for white LEDs).

Dunedin can be an enviable star sanctuary by shielding existing lights — and when safer, energy efficient Amber LEDs become more affordable, and once the NZTA (which co-funds street lighting) recognises their worth and updates  its guidelines, an intelligent and responsible changeover can be made. As the retrofit will affect the city for decades, lighting Dunedin smartly will benefit everyone.

To learn more, visit

Kyra Xavia is a freelance journalist who has written this piece on behalf of the Dunedin Dark Skies Group.


It would be ludicrous to throw ratepayer money away on expensive lighting so people can look at stars, when we currently can't even afford decent poles to put the lights on.

Especially considering even if we spend millions, star visibility still never ever be as good as if you drove 5 minutes out of town, or as good as 99% of the South Island.

Not to mention you'd destroy the view of the beautiful jewel clustered hills that are Dunedin city at night.

It would be ludicrous to throw ratepayer money away on maintaining all existing light poles when we might only need half of them (LEDs are a lot more effective than the current lights so fewer are needed for the same level of illumination)

It would be ludicrous to accept that this is just about "star visibility", whose reduction is just one symptom of a much greater problem, light pollution. I guess it just goes to show that education of the public on this subject really is needed.

It would be ludicrous to dismiss "star visibility" as a worthwhile goal, yet decry the loss of our "beautiful jewel clustered hills", and keep a straight face. That horse has bolted too, because LED streetlights (and they WILL come), regardless of colour or S/P ratio, are shielded by default. I'm afraid your only hope will be for Dunedin to hang on to its existing streetlights for as long as possible/practical.

Dunedin is very lucky to have not only an active astronomy society and observatory, but also the Dunedin Dark Skies Group who are advocating Dunedin to be a world leader in responsible night lighting. In contrast to many other places, New Zealand, because of its low population density, still has relatively good access to the night sky for its citizens, but still enjoying dark skies is difficult in many areas due to thoughtless use of unshielded street lighting. It is not only about enjoying the night sky of course. Increasingly attention is drawn to health aspects for humans as well as for animals, of artificial lighting. The Dunedin Dark Skies Group is doing a great job in collecting research results and disseminating the latest insights of this important issue to its citizens and to local government.

The existing street lights in Dunedin city are typically 10 to 30% efficient at turning electricity into light. Most of the remaining energy is emitted into the atmosphere as heat. Of that 10 to 30% that is turned into light, up to 60% is wasted by being spilled far beyond where it is required. The total cost of the energy for street lighting is paid for by the ratepayers of Dunedin or road users. NZ’s electricity generation still relies on fossil fuels in part so reducing street lighting electricity consumption is important from the climate change perspective.
LEDs are much more efficient in creating light and more directional in the light emitted resulting in less wastage. LED lamps are inherently sources of blue light which is filtered or converted into longer warmer coloured wavelengths. Current LED’s still have a high component of blue light.
Blue light is implicated in a range of ecological and human health concerns ranging from disruption of species to a range of serious health issues such as cancer, depression and obesity.
The cost for “beautiful jewel clustered hills that are Dunedin city at night” is too high a price to pay for occasional city nightscape photographs.

This is a great article in support of a great cause. There's no point upgrading Dunedins lighting unless we are going to do it in a way that is good for the city and the health of everyone living in it. Hopefully the upgrade will be done right.