There has been much debate internationally about whether new LED street lights with a colour temperature (CT) of 3000K (Kelvin) provide a more suitable solution than 4000K lights. CT indicates the colour of lights. As a general rule, the higher the CT, the whiter/bluer the light appears.
A number of environmental and astronomical groups say street lighting should be no more than 3000K, since evidence shows lights with a higher CT can disrupt the circadian rhythms of animals and increase skyglow.
On the other hand, research also shows perhaps a 20 per cent benefit in main road safety outcomes for drivers when whiter 4000K lights are deployed as compared to 3000K lights at the speeds and traffic volumes found on main roads. Underpinning this, leading US road safety researcher Dr Ron Gibbons said at an IPWEA conference last year there was a 30-40 per cent increase in the distance at which drivers recognised hazards with higher colour temperature lighting in standardised studies of target detection distance.
Considering these differing viewpoints, what street lighting are state and local authorities in Australia to deploy? IPWEA has developed a strategy that balances all viewpoints.
Concerns about 4000K LEDs
LEDs have been in the sights of different groups since large-scale deployments began in 2009.
Australia was an early adopter of LED street lighting. In the first big Australian LED deployment, more than 6,000 LEDs were deployed by the City of Sydney beginning in 2012 and these lights demonstrated significant cost and energy efficiency advantages over conventional lights. Others soon followed this example.
In the US, the use of LED street lighting is particularly contentious. In 2016, an American Medical Association (AMA) report recommended that all street lighting be no more than 3000K. The AMA report referenced the harmful environmental effects of LEDs with a CT above 3000K, but also suggested a possible link between these LED lights and damage to the human retina and eyesight.
The AMA’s recommendation and other similar recommendations have led many cities and council authorities worldwide to adopt their own ‘3000K or below’ approach. But a growing number of organisations such as the US Department of Energy and the Illuminating Engineering Society (IES) believe this approach is unsound.
Why a 3000K or below approach may be flawed in some circumstances
There is now a growing body of evidence suggesting 4000K lights are not harmful to humans. One important Australian study, in particular, casts doubt about the harmfulness of 4000K lighting to humans.
A joint 2019 study by Brisbane City Council, Energex and Queensland University of Technology found blue-light irradiance from LED street lights was just 1/100th of the recommended maximum exposure limit that would constitute a blue-light hazard. In other words, they were not dangerous.
Also in doubt is whether blue light from LEDs constitutes a ‘new threat’ to the environment. For example, in an opinion piece published by the IES, the author makes the valid point that the CFLs, mercury vapour and metal halide used in pre-LED street lighting also contained as high or a higher blue-light content than LEDs.
Taking into account this evidence and the driver-safety findings, deploying 4000K street lighting may be the best option in certain circumstances – especially if it can prevent injury and save lives on main roads where the greatest risks are.
IPWEA seeking the right balance
The recent IPWEA SLSC Model Public Lighting Strategy aims to balance the different viewpoints, environmental/safety and community concerns. IPWEA recommends 3000K for most residential roads and in parks, which constitutes approximately 70 per cent of all public lighting.
The strategy also recommends 4000K street lighting for main roads. This is based on maximising driver and pedestrian safety. The strategy also recommends using smart controls to dim lighting off-peak and the use of even lower CT lighting to mitigate adverse environmental effects in environmentally sensitive areas.