How does artificial lighting affect Bats?

Artificial lighting has a big impact on bats, since most species are nocturnal and rely on darkness for feeding, commuting, and roosting. The effects can be both negative and complex

Disrupts feeding – Many bat species avoid lit areas because they prefer darkness for hunting insects

Alters flight paths – Bright areas break up their usual dark travel routes, leading to longer, more dangerous paths

Raises Predation Risk – Lit areas make it easier for predators, such as owls, to spot the bats

Disturbs Roosting – Light near roosts can affect rest and reproduction

Is your ‘bat-friendly’ lighting, really friendly?

What most people call ‘bat‑friendly lighting’ is really an approach to lighting installations that minimises impact, not a type of fixture that bats actively seek out.

So how do we protect our friendly local neighbourhood bat?

Contrary to what ‘bat‑friendly lighting’ might imply, light itself is never bat‑friendly. In fact, research shows that all bat species demonstrate some degree of light aversion, though the strength of their response varies.

Research from some of the most knowledgeable authorities on Bats showed that the impacts of LED and sodium street lighting on bat activity along commuting routes – even at low levels of just 3.6 lux – slow‑flying species like lesser horseshoe bats (Rhinolophus hipposideros) and Myotis bats significantly reduced their activity. These bats avoided lit hedgerows, with emergence times delayed and commute paths disrupted (Street lighting disturbs commuting bats’ by Emma Louise Stone, Gareth Jones and Stephen Harris Current Biology 19, 1-5, July 14 2009, University of Bristol).

Faster flying bats (like Pipistrellus pipistrellus, P. pygmaeus, Nyctalus/Eptesicus) have been known to show little to no reduction in lit areas but it is acknowledged that tolerance does not equate to benefit.

The Bat Conservation Trust (BCT) has worked in conjunction with the Bats and Lighting Research Project by University of Bristol along with involvement from Natural England. Their evidence concluded that “Being nocturnal bats are among those species most likely to be impacted by lighting, although artificial light can impact all species and behaviours”.

So how do we make our lighting ‘Bat Friendly’?

It’s actually not difficult. Working along side well-established ecologists, lighting designers can formulate Lighting Strategies that ensure that a warmer more ecologically friendly light source is used. Specialised LED optics can be used to divert light away from key ecological corridors and the amount of time a light source is on also helps.

Are there any other bright ways of protecting ecology?

Light itself is not the only way to keep our biodiverse environment safe, a good engineer will look at the overall picture and see how blocking elements can be incorporated into the bigger picture, meaning your garden fence is not just a stopping point at the end of your garden but a defender of the environment!