Garden lighting: effects on wildlife

Night-time lighting either from security lights or decorative garden lighting illuminate our garden spaces after dark, but what about the effects on wildlife?

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Frogs seem to be attracted to light. Credit: RHS.

Quick facts

The breeding success of glow worms is adversely affected by artificial lighting
Bats show disrupted feeding patterns in lit areas
Robins extend their activity period in artificial light, feeding longer and singing in the middle of the night
Moths and nocturnal-flying migrating birds can be disorientated by light sources and urban areas

Lighting in gardens

Gardeners often use garden lighting to brighten up their garden at any time of year - from summer parties to winter viewings.

  • Lighting in gardens can illuminate particular features and create a welcoming place to sit in the evenings but can negatively impact on wildlife
  • Security lighting is another major use of light in gardens, positioned to catch the movement of visitors or intruders, often around entrances and the sides of buildings
  • Low-voltage, easy-to-install kits can be plugged into a pre-existing mains socket, and usually have smaller light fittings than mains electricity lighting, which is only really necessary for illuminating large gardens or big trees
  • A registered electrician must be used for all mains garden installations

Lighting and wildlife

The potential effects of artificial light at night (aka ALAN) on wildlife and the environment is often overlooked. Light pollution from inappropriately positioned security lighting is often the worst culprit but eidence suggests all forms of artificial lighting (including LEDs and halogen) can impact on wildlife. A paper published in 2020 concluded that light pollution is a driver of insect declines (pdf).

Impact on wildlife

Artificial light at night can impact wildlife in multiple ways, affecting navigation, physiology, breeding and general health. Although some wildlife might seem to come off as winners (e.g. bats hunting for prey around street lights), overwhelmingly the impact is detrimental. Below are just some of the recognised effects;
  • Nocturnal insects, including many moths navigate in part by natural light sources, such as the moon, and can become disorientated by artificial light, wasting energy, increasing their risk of predation and reducing their efficiency as nocturnal pollinators. However, it may not just be nocturnal species that are affected by light pollution. Artificial light at night disrupts circadian rhythms in both nocturnal and diurnal animals. For example, some moth studies have linked light pollution with steeper declines of nocturnal species while others have found steeper declines in diurnal species
  • Many bat species avoid lit areas altogether and although some bats are more tolerant and take advantage of the accumulation of insects at artificial lights to hunt, it can then open these species up to the risk of predation as well
  • Security lights may temporarily blind some animals and may even attract them, as appears to be the case with frogs
  • Lighting can act as a barrier for some species, fragmenting habitats, while for others artificial light is fatally attractive, becoming a sink for hundreds of insects each night
  • Garden birds are disturbed from sleep by sudden lighting and can begin singing before dawn. Robins especially seem sensitive to light and will extend their feeding period into the night where artifical light is present. Owls may find hunting more difficult in lit, urban areas and birds that prefer to start migration flights at night can become disorientated
  • Development and phenology of aphids and crickets is disrupted by night light. As with the impact of climate change, changes in phenology (timing of events in nature) can lead to mismatches between links in ecosystems such as host plants, pollinators, prey and predators
  • In lit areas, shorter periods of nightime darkness mean less time for foraging or hunting of crepuscular (dawn/dusk) or nocturnal species, reducing their temporal niche.
  • Light pollution is thought partly to blame for the decline of glow worms; the females emit low, greenish light to attract mates and even low level 'skyglow' from distant light sources such as floodlit playing fields or towns will lessen their breeding success
  • The type (frequency) of light seems to affect species differently. For instance, LEDs seem to attract more moths and flies, but fewer beetles than sodium lamps. And LEDs with cool white light (blue end of the spectrum) attract more insects than warm white ones. As a general rule insects are more sensitive or attracted to short-wavelength (UV, blue and green) than long-wavelength (orange, red and infra-red) light
  • As for light intensity, dim lights, such as warm white solar powered lights, are less likely to affect wildlife. But avoid coloured solar lights as these seem to confuse and attract glow worms
  • Under polarised light (aggravated by artificial light) mayflies and other aquatic insects can mistake impermeable non-aquatic surfaces for water and lay their eggs there where they will fail

What gardeners can do to minimize impact

Since artificial light in gardens disrupt natural behaviour for a range of wildlife it's important to retain some dark areas and also question whether you really need lighting. The trend for lighting up gardens as an extension of our living space may seem an inviting one but needs to be done with great care. A garden can be just as magical a place enjoyed in moonlight or simply with the aid of torch!

Tips for reducing impact

  • Position lights as low as possible and aim them downwards or to where they're needed. When angling lights make sure you think about how it impacts on your neighbours too (such as not glaring right into their windows) and always position them considerately
  • Fit hoods over the light to reduce light pollution of the night sky
  • Turn garden lights off when not in use or use PIR motion sensors or timers for essential or security lighting so they only come on when absolutely necessary
  • Choose low-intensity lighting and warmer hues (warm white, yellow or amber): solar lighting is cheap, safe and emits a dull glow suitable for garden use
  • Encourage local councils to adopt switch-off schemes for street lighting: even part-night lighting instead of full-night lighting has been found to reduce negative impact on the behaviour of moths

Artificial lighting and human health

Measures to reduce negative impacts of lighting on wildlife are also likely to be beneficial in reducing adverse impacts on people - see Chapter 4 page 4 'Light pollution and health' from the UK Government's Annual Report of the Chief Medical Health Officer 2017: Health Impacts of All Pollution - what do we know?

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