By Rhian Newman
Britain is a nation of birders. Thanks to TV shows such as the BBC’s Springwatch, bird feeding and watching is more popular than ever. More than half the UK adult population goes to feed the birds at least once a week.
The British Trust for Ornithology recently asked members of the public to survey the number and variety of birds in their garden. Participants were asked to record the first arrival of each bird species to their garden feeder, one hour after daybreak. They were also asked to record how many sources of artificial light were within 50m of their home, and exactly how near they were. So not only was the trust able to collect valuable data on the distribution of bird species, but it was also a useful exercise to increase public awareness of a much-overlooked environmental pollutant: light.
Ruining nature’s rhythms My research, in partnership with the Centre for Environment, Fisheries and Aquaculture Science (Cefas and Eco-Explore, has examined the impact of artificial light at night on the behaviour of freshwater fish. Why, many people have asked me, do fish care about street lighting? They care because it alters the natural pattern of light and dark in their ecosystem, affecting their daily behaviour, and that of their prey. Light pollution is among the fastest growing man-made pollutants of the natural environment, and surveys such as these highlight the need to address it.
Over the past 60 years, the number of outdoor lights across the UK has drastically increased. There are more than 7.5m lights lining motorways and illuminating residential streets, a figure that increases by 3% annually in the UK and by 6% around the world.
But despite how many artificial lights there are and how quickly they are proliferating, the recognition that light can be a problem has come only recently. There are major gaps in our knowledge about its effects on most animals. From the limited science we have, it’s been suggested that artificial lighting affects the behaviour and even physiology of a huge number of species groups. For example, by disorienting sea turtle hatchlings, affecting the choice of nest and breeding success of birds, or causing physical changes in the eyes of salamanders. Many organisms have been affected by humans' widespread disturbance of the natural patterns of light and dark.
Street lights change hue Most streetlights in the UK are low-pressure sodium lamps (LPS). These produce light at a narrow band on the visible spectrum, about 590nm, which is yellowish in colour. These are steadily being replaced by a variety of new technologies, purportedly for cost savings or environmental reasons. However, while these lights may be more eco-friendly to run, the brighter, whiter light they produce may be more intrusive to nocturnal species.
According to a seminal review by the Royal Commision for Envionmental Pollution in 2010, which set the agenda for light pollution research, the shift from LPS to more modern lighting is not just down to bean counting local councils. The narrow band of light produced by LPS allows only poor colour discrimination, which makes it hard for us to see. High-pressure sodium (HPS) lamps, which produce a wider spectrum of light more suitable for human vision, are commonly used alternatives. HPS lamps are also more compact, and so are easier to shield to reduce light bleeding in unwanted directions. Two other types of lamps considered next generation replacements for street lighting are metal halide and light-emitting diode (LED). These are extremely energy efficient and have a long lifespan, with LED lights able even to be powered by solar or wind energy generators.
According to a recent study in the Journal of Environmental Management, the spectral properties of different types of lamps determines the degree to which their light pollution infiltrates their surroundings. The effects of streetlights on the photoreceptors of a human eye were used as a model. The degree to which the lamps were said to be pollutants was dependent on the level of response seen in the photoreceptors of human eyes – the more intrusive an individual would find the light, the more polluting it was said to be. The study found that the LPS lamps now being replaced were the least polluting, while new LED lamps were the most polluting due to the blue cast of their light. So the move from LPS and HPS to next generation lamps seems likely to generate more light pollution, with greater environmental effects.
As most of Britain’s street lamps reach the end of their life and are due for replacement, the coming years present and excellent opportunity to try an minimise the environmental impact of these millions of artificial lights. How wildlife react to these new lights has not even been considered, as current studies are based on HPS/LPS lamps. It’s vital that we understand, before this new technology is rolled out countrywide, their ecological effects.
So we shouldn’t restrict our studies and debates about street lights to just potential problems for humans, austerity-inflicted council cuts, and possible crime or accident rates. The lamps that light the way as we walk home at night affect the other species too – so before we make them even brighter, we should be trying to find out how.