Safer street lights chosen for Tauranga

The much truer colours of LED lamps compared with the orange glow from old high-pressure sodium lamps in an adjoining street in suburban Auckland.

LED street lights that had less effect on wildlife sleep cycles will be used on Tauranga's quieter suburban streets.

City council transportation manager Martin Parkes was responding to a Bay of Plenty Times inquiry about which LED lamps would be used to light Tauranga streets.

The council planned to spend $5.5 million in the 2017-18 financial year to convert a big chunk of the city to LED lights, with another $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, with a minimum subsidy of 50 per cent applying after that.

Tauranga had largely adopted the same system as Dunedin which favoured replacing its traditional high-pressure sodium lamps with LED bulbs that let off a warmer white light.

These 3000 Kelvin lamps interfered less with the circadian or sleep cycle of wildlife than the much brighter white light from 4000 Kelvin lamps.

Leading New Zealand astrophotographer Dr Ian Griffin advocated 3000 Kelvin LED lamps, with light spillage shields to prevent the upward throw of light. The alternative 4000 Kelvin LEDs were intense and quite bright and made a big difference to insects, he said.

Mr Parkes said 4000 Kelvin was a better colour temperature for transport visibility and road safety and the council favoured installing those LED lamps along main traffic routes.

"In residential areas, we will be using 3000 Kelvin."

Mr Parkes said the LED package included a central management system that would allow the council to dim street lights when most people were asleep, but keep them brighter at key spots such as pedestrian crossings. The system also identified where a bulb had failed.

He said there was a lot of upward light spillage from the sodium lamps. Direct the light from LED lamps downwards and dimming to 50 to 75 per cent of peak brightness would substantially reduce spillage into the sky.

The council had begun replacing the characteristic orange glow from sodium lamps with the clear white light from LED bulbs, starting in Welcome Bay.

Advantages of LED lamps included substantially lower energy costs, better light quality, clearer colour contrast and greater pedestrian security.

Kelvin temperature scale
- Brainchild of Glasgow engineer and physicist William Thomson, 1st Baron Kelvin (1824-1907)
- One of the three best-known scales used to measure temperature, with Fahrenheit and Celsius.
- The scale began at the temperature at which molecules stopped moving or "infinite cold".
- Popular in scientific applications because there were no negative numbers.
- Typically used in lighting to pinpoint colour temperatures.