Some effects of modern lighting technologies on bat activity and potential for mitigation

  • E G Rowse

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Over the past two centuries, artificial light at night (ALAN) has increased globally, with rapid growth in the last 60 years due to the rise of urbanisation and industrialisation. Among the main contributors to ALAN are street lights because of their ubiquity across the world. The number of street lights is not only increasing, but their spectral signatures are also changing; currently, there is a trend to use broad-spectrum lights, such as light-emitting diode (LED), metal halide (MH) and fluorescent (FL) lights. These switch-overs in technology may result in both financial and environmental improvements, but ecological impacts have not been fully considered.
I explored the ecological impacts of ALAN, by investigating the effects of street lighting on bats, which have the potential to be affected by street lights due to their predominantly nocturnal behaviour. Bats are often described as being light-opportunistic (fast-flying bats that feed on the increased number of insects attracted to the light) and light-averse (slow-flying bats that avoid lit areas probably due to the perceived risk of predation).
Switching from low-pressure sodium (LPS) to LED lights did not affect the activity or the number of feeding buzzes of those bats found in close proximity to street lights at 12 suburban sites across south Britain. From a conservation viewpoint, these results are positive as they show that LED lights are not affecting the local bats any differently from LPS lights. However, most bats recorded were light-opportunistic species, where artificial lighting seems to have less effect than for slow-flying species.
In addition to installing LED lights, many local authorities are also implementing cost-saving strategies such as dimming. Reducing the light intensity by 25% of its original output did not significantly affect the number of passes of light-averse (Myotis spp.) or light-opportunistic species (Pipistrellus pipistrellus). This is a particularly encouraging result for light-averse species, many of which are often described as threatened. It might be possible to use dimming to achieve a light intensity that reduces the ecological impact of street lighting that is acceptable for human vision and also offers cost benefits.
In addition to affecting local insect populations, the spectral emissions of street lights may also vary in relation to the spectral sensitivity of bats eyes, thereby having implications for street lighting guidelines. British bats have UV-transmissive lenses, so are sensitive to UV wavelengths that are emitted from FL and MH, but not LED, lights. The results from all three experiments, in addition to research in the current literature, suggest that where street lighting is necessary, LED lights should be installed as they can be adapted to mitigate some of the negative ecological impacts of ALAN.
Date of Award28 Nov 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorGareth Jones (Supervisor) & Andy Wakefield (Supervisor)

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