New LED street lights across Devon will be dimmed during part of the night – to help reduce their potential impact on insects.
The county council is currently rolling out upgrades in residential areas and says all of its 79,000 illuminations will be converted from traditional sodium bulbs to the energy-efficient equivalent by next year.
It reduce their carbon emissions of by 75 per cent – more than 15,000 tonnes each year – the equivalent of taking 8,000 cars off the roads, writes Local Democracy Reporter Ollie Heptinstall.
But a recent study suggests the ‘eco-friendly’ illuminations, which produce more of the blue light mainly seen by insects, are more harmful to them than sodium bulbs.
Researchers at the UK Centre for Ecology and Hydrology found the number of moth caterpillars in hedgerows along rural English roads was 52 per cent lower under LED lights and 41 per cent lower under sodium lights when compared with nearby unlit areas.
In grass margins, the moth caterpillar population near LEDs was a third lower than in unlit areas, while sodium lights had little effect on abundance.
Writing to the Devon County Council’s (DCC) cabinet, Councillor Alistair Dewhirst said: “The energy efficiency of these lights is clearly a fact and is helping to improve our carbon efficiency…but it would appear to be at the expense of our insects.”
He asked what the council will be doing to ‘mitigate the harmful effects on our insect population’.
In a written response, Cllr Stuart Hughes, cabinet member for highways, said: “The rating of the new lamps is 3,000K (kelvin), which is very similar to the sodium lamps they are replacing.
“Insects are generally attracted to lighting above 3,000K, therefore any possible effect on the insect population is argued to be neutral when the new lamps are run at 100 per cent brightness all night.
“However, in mitigation, the lighting will operate as part-night lighting for the majority of areas and in addition dim to 75 and 50 per cent brightness later into the night.”
Cllr Hughes added: “DCC is also extending its management software in new installations where possible, which will give much more control on future dimming.
“However, we will keep this under review as greater understanding of this topic develops.”