NIWA scientist throws light on the Red Zone

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Christchurch’s Red Zone is to be the focal point of a scientific experiment involving street lights and insects over summer.  

NIWA freshwater ecologist Dr Michelle Greenwood is trying to find out how a change in the colour spectrum of street lights is affecting insects that live in and near freshwater. [Photo: Simon Hayes, NIWA]

Street lights throughout New Zealand are rapidly being converted from mostly high pressure sodium lights, which emit a yellowish light, to low energy, light-emitting diodes or LED lights which emit a bluer light.  

In addition to substantial cost-savings, LED lights are also reported as providing better colour differentiation and visibility.  

However, Dr Greenwood says little is known about how the colour change will affect insects which are indicators of healthy urban waterways.  

“A lot of insects are more sensitive to the blue end of the colour spectrum which means they could be more attracted to the new street lights,” she says.  

“If they are attracted to light, they are attracted away from normal activities. They might just fly around and around the light until they’re exhausted and die.”  

Dr Greenwood’s experiment, which is being supported by Christchurch City Council, is taking place next to the Avon River so she and her team can look at the insects emerging from there and other urban waterways to see how they behave around the lights.  

Blue light laboratory in the red zone

“The Avon is tidal so it may mean that there are different responses at different locations so we are hoping a pilot study this summer will guide further trials later in the project.  

“The really great thing about this is that by using areas in the Red Zone we can carry out our experiments in a real-life, operational scale setting. It’s an area where the houses have been removed but the street lighting infrastructure remains intact.”  

The first test will be a pilot study where sheets of clear perspex coated in a sticky substance are mounted next to the light to catch insects. These will be replaced daily.  

“LED lights come in different colour temperatures so by changing the tones used in the street lights next to waterways, or by dimming them, we are hoping to find out what the ecological gains might be versus the energy costs.”  

Colour and direction effects on insect behaviour

For several months, as the LED conversion has been taking place, Dr Greenwood has been taking photos of Christchurch from the Port Hills.   

“I thought I’d see the city change from yellow to blue, but what I’m seeing from above is almost the city disappearing because the new lights are so well shielded. There is a lot less light to see above the street lights and that’s really positive.”  

There are also two other components of the three-year collaborative project. 

They include the creation of an interactive web page where users can change the lighting of areas in Christchurch to see what the city would look like under different scenarios. Dr Greenwood says this may pinpoint critical areas around waterways where there are a lot of lights where different lighting options may be beneficial to insects as well. The maps could also identify areas with better night sky visibility.  In addition, Scion is developing drone-mounted sensors that will map light temperatures at an “insect scale”.   

“Urban skies and waterways are ideal systems in which to trial our tools and develop recommendations to minimise the impacts of large-scale streetlight conversions.”  

The project is funded through the Ministry of Business, Innovation and Employment’s Endeavour Fund and undertaken in conjunction with Scion, the University of Canterbury, Christchurch City Council, NZTA  and LINZ. 

There are about 370,000 street lights across New Zealand, of which about 40,000 are in Christchurch. An Energy Efficiency and Conservation Authority (EECA)-commissioned report estimates that switching to LED could save $10m in operational costs each year.  

Contact 

Dr Michelle Greenwood, NIWA freshwater ecologist 
Ph 03 343 8061  

Research subject: EcosystemsPhysicsRivers