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    How artificial light can be adapted to protect light-sensitive bats

    The introduction of artificial lighting brings many benefits to urban environments. It improves visibility, increases the sense of comfort and safety, and can even be used as a powerful tool to create experiences and change perception of spaces.

    All these benefits can only be achieved using the right light source with the right quality. Poor quality lighting, both traditional and LED, can have various negative consequences on the well-being and comfort of both nature and people. Among these drawbacks are increased light pollution and sky glow, discomfortof residents in cities caused by glare, harsh and uncontrolled lighting, and the negative impact on biodiversity.


    This article explores the latter topic: the consequences of artificial lighting on biodiversity; in particular on bats. It describes measures that need to be put in place to ensure that these animals are not disturbed by artificial lighting during feeding and general night-time activities.


    The impact of artificial light on bats


    Though not everyone is aware of this, bats are extremely important to a balanced ecosystem. They control numbers of potentially irritating or harmful insects, and are highly effective in controlling agricultural pests, which can lead to a reduced need for pesticide sprays. They are also robust natural indicators of environmental health, as changes in bat populations indicate changes in aspects of biodiversity. The Habitats Directive published by the European Commission covers all bat species living within the European Union. The Directive requires all Member States to undertake positive measures to ensure that their bat populations are afforded a favorable conservation status.


    Investigations carried out by a number of associations, such as the Bat Conservation Trust, have found that artificial light affects night-time movement and feeding of bats. Furthermore, it was found that different species react differently to artificial light, which can result in a significant disturbance of the overall ecosystem by giving unfair advantages to species that are less afraid of artificial light.


    In short, light can have an impact on bats’ commuting routes. For example, lit roads can act as a barrier that bats either cannot or dare not cross. Light can also have direct or indirect effects on breeding colonies, hibernation sites and roosts. During research conducted in 2017 by the Bat Conservation Trust, it was found that white light LEDs dissuade slower flying species from drinking at cattle troughs, and even the drinking behavior of faster flying species was impeded.


    A seven-year study at eight different sites


    To examine these impacts more closely, we initiated a study that tested the response of three species of bat to three different experimental light spectra in an otherwise dark and undisturbed natural habitat. Over seven years, research was conducted at eight sites in the Netherlands. Light posts were set up that emitted either white light or two different light recipes. The results of the research showed that certain species are very much afraid of artificial light and try to avoid it at all costs, but when applying the dedicated recipe with a selected spectrum, their behavior was the same as during full darkness. Click here to download the white paper which explains the methodology used and the primary results obtained.


    A light recipe to provide an optimal ecosystem for bats


    In line with research findings, a new light spectrum was designed for animals that are distracted by short wavelength light. It displays minimal attraction for insects. Bats behave the same way as if it was full darkness, which therefore helps maintain the balance of the ecosystem by providing equal opportunities for all species. Lit roads don’t act as borders or obstacles to be crossed at night. At the same time, people have sufficient light to operate or drive safely.

    Rare bats in Nieuwkoop get the benefit


    Thanks to its rare and special flora and fauna, Zuidhoek in the municipality of Nieuwkoop in the Netherlands is part of the Natura 2000 network. The municipality decided to turn an old camp site into a residential area, but prior to construction work starting, they were obliged to assess the area’s flora and fauna. They discovered that it is an important feeding area for some rare bat species. Before proceeding with the housing program, they therefore had to put some conservation measures in place, including lighting that would not disturb the nocturnal feeding activity of the bats. The municipality selected the dedicated light recipe developed for bats by Signify. It does not impact the behavior of the bats, but ensures sufficient illumination for the area’s human residents. Click here  to read the case study.


    In summary, initiatives like the light recipe developed to ensure undisturbed night time for bats,  show that while future-proof lighting has a clear goal to improve energy efficiency, it can also contribute to the conservation of nature.