Tauranga is to transform the way it lights its streets by spending $11.5 million to convert to LED white-light lamps.
Instead of the characteristic orange glow emitted by traditional high-pressure sodium lamps, the city will be bathed in a more natural white light, with improved safety and big energy savings.
But questions remain to be answered before the city council signs off on which LED (light-emitting diode) system it adopts, including possible impacts on the sleep cycles of wildlife.
"We are seeking clarification on the way forward from an industry expert next week," council transportation manager Martin Parkes told the Bay of Plenty Times.
The council planned to spend $5.5m in the current 2017-18 financial year to convert a big chunk of the city to LED lights, with the other $6m spread over the following two years.
The New Zealand Transport Agency was picking up 85 per cent of this year's bill, leaving $825,000 to be funded by ratepayers. A minimum subsidy of 50 per cent would apply after that.
Mr Parkes said the LED package would include a central management system that allowed the council to dim street lights when most people were asleep, but keep them brighter at key spots like pedestrian crossings.
"A lot of councils dim street lights after midnight because there are not a lot of people around."
Tauranga astronomers were particularly interested to see what LED system the council ended up installing. They want to minimise light spillage from the much brighter LED bulbs.
Mr Parkes said there was a lot of upward light spillage from the sodium lamps. Directing the light from LED lamps downwards and dimming to 50 to 75 per cent of peak brightness would substantially reduce spillage into the sky.
Tauranga astro-photographer David Greig said he was no expert but there had been a lot of concern about the potential for LED lights to cause more light pollution.
Their cameras filtered out the orange wavelength light from sodium lamps but did not have the same ability with white light LEDs. LED lamps needed to have shields that prevented the upward throw of light, he said,
A leading New Zealand astrophotographer and director of Otago Museum, Dr Ian Griffin, said that if the Tauranga City Council chose lamps with light spillage shields it would in principle be an improvement for astronomers.
He said the Dunedin City Council had opted to convert to slightly more yellow and warmer LED lights, with shields that forced the light downwards.
Dr Griffin said the alternative blue light (colder) LEDs were quite intense and quite bright and made a big difference to insects.
The Dunedin City Council's transportation strategy manager, Nick Sargent, said the city was seeking permission to use 3000 kelvin lamps because it was a warmer white light.
"The whiter the light, the more it interferes with wildlife."
Mr Sargent explained that the higher the kelvin number, the more it interfered with the circadian or sleep cycle of wildlife. "If it is a very bright white light, it could have that effect."
Mr Parkes said the Tauranga City Council was still in the process of determining whether to opt for 4000 or 3000 kelvin lights, and was seeking clarification from an industry expert.
Advantages of white light LED street lamps
- Lowers energy usage by 30 to 60 per cent
- Less maintenance
- Better light quality
- Clearer colour contrast improves driver reaction times
- Greater pedestrian security and comfort in public areas