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Dunedin sees the light – and the dark

Dunedin Street lighting

In recent years Dunedin City Council has taken a thorough approach to the planning and procurement of its street light renewal, canvassing both the possible adverse effects and the opportunities afforded by a move to LEDs.

The work has attracted the support of the vice president of the International Dark-Sky Association. Council staff presented the approach at the recent 4th International Street Lighting and Smart Controls Conference in Sydney. Anja McAlevey explains.

Dunedin’s 15,000 street light luminaires are reaching the end of their useful life. Most were installed during the early 1990s and the failure rate and maintenance costs are increasing. Like many other local authorities, Dunedin City Council (DCC), working with NZTA, is undertaking a citywide renewal of the current high-pressure sodium street lights to light-emitting diodes (LEDs), including citywide installation of a central management system (CMS).
The contract for the whole renewal has recently been awarded to Broadspectrum with estimated capital costs of $12.5 million. Installation should begin in July this year and be completed by December 2020.
Typical for most LED renewals, the business case shows clearly that this is a worthwhile project to invest in, with a payback period of nine years, estimated energy reduction of 56 percent and maintenance/cleaning cost reduction estimated at between 75 to 90 percent. This translates into massive monetary and environmental benefits.
Alongside these benefits, wider opportunities and costs were considered in planning the Dunedin renewal. DCC’s strategic vision includes a night sky city aspiration. This recognises the importance of the night sky in Dunedin and aims to improve night sky vistas.
Dunedin, like much of the lower South Island, enjoys spectacular night skies, including views of the Milky Way and the Aurora Australis. There is an observatory right in the middle of Dunedin and a small, yet highly-engaged, group of dark sky advocates.
The night sky city aspiration became a catalyst – turning a straightforward asset renewal into an exploration of the opportunities of LED technology, and the possible adverse effects of moving to LEDs.
There has been much debate in recent years on the possible effects of LED street lights, particularly as they generally have more blue light than incumbent technologies (including the 4000 kelvin luminaires preferred by the NZTA).
The Royal Society of New Zealand Te Aparangi recently released an expert advice paper Blue light Aotearoa: Impacts of artificial blue light on health and the environment. The Royal Society identified that this is a subject with many unknowns and research gaps. Research into the potential night sky, human health, wildlife and road safety effects of moving to LEDs is ongoing worldwide.
With this uncertainty in mind, careful planning was undertaken for the Dunedin renewal. DCC set up a Night Sky Advisory Panel made up of key stakeholder representatives to provide advice and input on lighting projects.
Advice was also sought from various organisations. These included other councils, NZ Police, DCC’s Disability Issues Advisory Group, the Ministry of Health, the Department of Conservation, wildlife experts from the University of Auckland Centre for Biodiversity and Biosecurity, Flagstaff Dark Skies Coalition (Arizona, USA) and the International Dark-Sky Association. Expert consultant advice on street lighting was
also secured.
A range of options was considered for LEDs in Dunedin – using the colour temperature or kelvin of the lights as a proxy for blue light content (the lower the kelvin, generally the lower the amount of blue light). DCC explored different colour temperature LEDs, luminaires pre-programmed with a dimming profile, and different-sized control systems.
It settled on a solution that met the International Dark-Sky Association (IDA) guidelines, with very little compromise on luminaire price and energy savings. Three-thousand kelvin luminaires and a CMS will be installed citywide, including on state highways. Lower kelvin luminaires may be installed in some areas of particular night sky or wildlife value – this is yet to be determined.
Dunedin is far from alone in installing 3000 kelvin luminaires in this country. Hamilton has completed its renewal to 3000K on Category P and Category V roads (excluding state highways), and Wellington is installing 3000K on residential roads. Many councils in the lower South Island have chosen 3000 kelvin luminaires.Dunedin Street lighting
The decision to install a citywide CMS in Dunedin was driven by the cost savings of installing the CMS and new luminaires at the same time, as well as by the many benefits of a CMS. Enhanced asset knowledge and management will reduce maintenance costs and improve road safety. The ability to control light levels will enable higher lighting levels when needed for road safety, and lower lighting levels when fewer people are on the roads, minimising any adverse effects of light at night.
Lighting levels can be tailored to specific places and times – this may be around the Observatory, at the habitat of a particular species during a sensitive phase, during an astronomical event of particular note, during the Dunedin Midwinter Carnival, or during major events or emergencies.
The CMS will also provide a platform for future smart city systems, incrementally, and with minimal cost. These could include: digital street signs for parking, speed or travel time; traffic counters; sensors for parking, alerts that rubbish bins need emptying, temperature, pollution or noise monitoring; as well as future applications not yet conceived of.
DCC put considerable thought into the procurement phase of this significant long-term investment. A market sounding event was held to share information with industry suppliers, designers and installers. A long-term integrated Design, Build, Operate, Maintain contract was chosen. This was partially to secure one point of contact and responsibility, hoping to avoid miscommunications, variations, cost blow-outs and delays.
It was also designed to attract world-class expertise and incentivise the contractor to do a good job. The additional upfront work and attention to detail needed for this delivery model should pay off over the course of the renewal.
DCC also conducted a trial installation of short-listed tenderers’ lights. They were evaluated for subjective performance – with various “look and feel” visual comfort parameters, such as glare and light cut-off. Public feedback was sought on the lights. Real effort was put into understanding residents’ opinions by door knocking and delivering a survey by hand: 76 surveys were received back from residents (out of an area with 200 houses).
Surveys have also been undertaken on light levels and sky glow to aid understanding of the change to LEDs. The light level on every street in Dunedin with street lights was recently measured, using road-speed vehicle-based dynamic measurement techniques. This survey will be repeated after the renewal. This lux data will help determine whether there is sufficient light provided by the LEDs and will provide factual measurements about how lighting levels have changed with the LED installation.
Sky glow has also recently been measured in several locations around Dunedin. This survey will be repeated after the LEDs are installed to show how night sky vistas have changed. These surveys will inform both decision-makers and the public, and enable conversations based on fact and scientifically-robust measurement, rather than on subjective opinion and speculation.
For Dunedin, this is more than just a lighting renewal project. The primary objective of road lighting is safety, but this infrastructure project has been carefully crafted to protect the night sky for residents and visitors, to minimise potential adverse effects, and to grasp the opportunities of LED technology, including providing a platform to help Dunedin grow into a smart small city.

  • Anja McAlevey is senior transportation planner, transportation planning, at Dunedin City Council.

This article was first published in the June 2019 issue of NZ Local Government Magazine.

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