What you need to know about LED lighting in bat nesting sites
Key lighting scheme considerations needed to account for lighting pollution in bat nesting areas
Bat numbers have been declining over the past 100 years and as a result there have been a significant number of habitat regulations put in place, both international and domestic, for the protection of all bat species and roost sites.
There are a number of negative impacts associated with artificial lighting on bat habitats. For instance, artificial lighting can cause disturbances to bats at the roost, affect migration patterns, and affect feeding behaviours.
Due to this, if bats are suspected to be present on a site, ecological advice should be sought, and survey data should be collected in advance of any lighting design. Consideration must be taken in relation to the importance and sensitivity levels of bat features or habitats and it may be appropriate to redesign or limit lighting accordingly.
Establishing ecological site significance
The detection of bat presence on your site is usually done through seeking advice from an ecologist, however this can also be achieved through consulting local sources of ecological information, for instance through local authority planning portals or Defra’s Magic Map.
Ecologists often carry out daytime and in some cases night-time bat surveys in order to assess the importance of the sites features and habitats to bats.
Mitigating artificial lighting impacts on bats
If it is established that bats may be impacted by your project, this must be fully considered within your lighting scheme proposal.
In key habitat areas, lighting must be avoided. These areas include roost entrances and associated flightpaths, habitats used by large numbers of bats, those inhabited by rare species or areas home to highly light adverse species.
In other locations of significance for bats on site, mitigation methods must be applied in order to reduce lighting to a minimum. This can be done through setting acceptable lux limits as suggested by ecological guidance, and through implementing dark habitat buffers.
At Hilclare, our lighting experts will prepare a full lighting scheme that takes into consideration glare and the illuminance (lux) levels required at your site, to ensure your project is compliant with conservation and planning legislation and policy.
Appropriate luminaire specifications for bat nesting sites
- Luminaires shouldn’t contain UV elements. This means that metal halide, flourescent sources should be avoided.
- Where possible LED luminaires should be used due to their lower intensity, good colour rendering, sharp cut off and dimming capabilities.
- A warm white spectrum (ideally <2700Kelvin) should be used to reduce blue light.
- Luminaires should feature peak wavelengths greater than 550nm to avoid the element of light most disturbing to bats.
- The use of specialist bollard or low-level downward directional luminaires to retain darkness above can be considered. This however can create unacceptable glare, poor illuminance efficiency, a high upward light component and insufficient facial recognition and so their use should be as directed by the lighting professional.
- The height of columns require careful consideration so as to minimise light spill.
- Luminaires shouldn’t have an upward tilt so as to ensure there is little to no upward light distribution.
- Only luminaires with good optical control and an upward light ratio of 0% should be used. (For more detail see the ILP guidance for the Reduction of Obtrusive Light)
- Any external security lighting should be set on motion-sensors and short (1min) timers.
- Streetlights can be placed so that the back shields are adjacent to habitats or optics can be selected that stop backlight, thus directing light into the task area where required. Hilclare’s Sancha streetlight is a great solution for this application as you can select the correct beam angle to ensure that the light is directed towards its intended target as opposed to any unnecessary light being directed upwards or outwards towards potential nesting areas.