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Steps should be taken to mitigate the effect of LED street lamps on nocturnal insect populations, a Dunedin researcher has said.
The advice comes after a British study, published in the August edition of the Science Advances journal, found evidence that street lights caused declines in moth caterpillar numbers.
LED street lights like those installed in Dunedin in recent years had the largest effect with a 52% drop in caterpillar numbers compared with unlit areas.
High-pressure sodium lights, the technology used in Dunedin before the LED rollout, caused a lower decline in caterpillars at 41%.
Royal Society Rutherford Discovery fellow Dr Barbara Anderson, who is based out of Otago Museum, said while there had not been similar research done on native species in New Zealand, the effect of LED lights on insects in general was well known.
The lights had an impact on moths and other nocturnal insects because they emitted high levels of blue light.
Moths were particularly affected because their eyesight was different from that of a human, seeing more colours to the blue and ultraviolet end of the colour spectrum.
‘‘So the moths are ... thinking that it’s daytime if there is blue light at night.’’
This confusion could drastically change the behaviour of moths.
‘‘They’re not ... going around pollinating plants, mating, laying their eggs, reproducing, all of the things they would normally be doing.’’
However, Dr Anderson said she was not saying LED lights should go, as they had other benefits including lower power consumption and reduced light pollution.
Instead, steps should be taken to mitigate LED lights’ effects on nocturnal insects, she said.
The colour of LED lights is measured in Kelvins (K); a higher number is towards the blue end of the spectrum, and a lower number means emitting redder light.
Mitigating steps could include dimming lights during low-usage times, and switching lamps to lower Kelvin units over time as replacements are needed, Dr Anderson said.
Rules could be put in place for new developments limiting the new street lamps to those at the redder end of the spectrum.
Closer to home, people could look to minimise light pollution at their own properties, eliminating lights that were not needed and connecting others to sensors or timers.
The majority of new streetlights installed in Dunedin are rated 3000K.
Lights rated at 2200K have been installed in more rural areas such as Waikouaiti, Karitane, Waitati, Warrington, Seacliff, and locations on Otago Peninsula.
Other cities in the country have opted for bluer LED lights, Auckland and Christchurch both installing 4000K bulbs.