24-09-2021 | | By Sam Brown
Recent studies on British wildlife have shown that LED street lights may be affecting the ecology of hedgerows. Why are traditional streetlights being replaced with new LED variants, how and why are these new lights affecting wildlife, and what other challenges do LED streetlights present?
For those born before the 2000s, streetlights have always been a warm amber colour due to sodium-vapour lamps. These lights come in two main varieties, low pressure and high pressure, and the technology primarily found in the UK is the low-pressure variety. Such lamps utilize a low-pressure gas (argon, neon, or a mixture), along with a small piece of solid sodium that is melted and vaporized when turned on. Once vaporized, very little energy is needed to excite the sodium (making sodium lights very energy efficient) and emit a very narrow frequency range of light (similar to a laser).
While these lights have been ideal for the past 70 years thanks to their efficiency (compared to other old lamp technologies), they are being replaced with LED variants. Many believe that these lights are being replaced for the sake of efficiency, but this is not entirely the case as modern low-pressure sodium lamps are only slightly less efficient than LEDs (37~120 lumens/watt compared to 50~160 lumens/watt).
One reason for replacing streetlights with LEDs is that older streetlights only produce yellow light, hindering visibility for pedestrians and drivers. Research has shown that LED lights (which produce white light) can improve peripheral vision at night, reduce braking distance, and help drivers see obstacles better.
Another reason for replacing street lights with LEDs is that LEDs offer directionality which helps to keep light away from the upper atmosphere. This can be highly advantageous for astronomers using high-end telescopic equipment who need to have clear skies with minimal light pollution. However, it should be noted that sodium lights can easily be filtered out from telescopes due to the narrowband nature of low-pressure sodium lights, and LEDs are ironically harder to filter (if even possible).
While LED streetlights provide greater efficiency and better visibility, research on these lights shows signs that they may not be as great as once thought.
Recently, researchers have discovered that hedgerows with LED streetlights have significantly less wildlife, including insects and mammals. It has been known for decades that artificial light upsets nature in general, but the introduction of LED lights sees the most significant change with as much as a 50% reduction of insects.
Unlike older sodium lamps, while LED streetlights emit a wide range of different frequencies, including the blue spectrum, it is well known that blue light is highly damaging to natural cycles. As such, exposing hedgerows to blue light via white LEDs negatively impacts nocturnal wildlife, which prefers darker areas. Furthermore, there is documented evidence of increased rates of depression in those who live next to LED streetlights compared to those who live next to older sodium lights.
One solution to improve conditions around LED streetlights is to include blue light filters. The resulting light would be yellow (just as in earlier lamps), and this light would be less harmful to nocturnal wildlife and people in general. However, using a filter would decrease the lamps efficiency and this fall in efficiency could potentially see sodium lamps take over.
Another method is to dim streetlights between certain hours or during low traffic, as Devon council will be experimenting with. According to the council, the replacement of the older lamps wills see carbon emissions reduced by 75%, but in light of the recent reports on impact with wildlife, Devon will dim their lights during late-night, where there is minimal traffic. Overall, replacing streetlights with LED variants helps to reduce the amount of CO2 produced via electricity production, and white LEDs have been shown to improve driving safety. However, authorities should also consider both the environmental and mental wellbeing of those who live in the vicinity of white LEDs.