Protecting local bat populations through careful lighting design

Wherever there is human development, so follows artificial lighting. This increase in lighting has been shown to have adverse effects on our native wildlife, in particular those species that are active during the hours of darkness. It is crucial then, that development needs to carefully consider what lighting is really necessary, and where required look to mitigate the effects of this lighting on wildlife and the wider ecosystem.

There is also an energy component to this, light going into the sky wastes energy that could be used more efficiently elsewhere or not generated at all.

How smart solutions in Electrical Engineering Design are changing our approach to external lighting in developments.

Of the 10 species noted throughout the island, a number of these are listed as threatened/endangered.  Due to this, developments, where bat species are present in the environment, require a special derogation licence to allow development, and in addition to this mitigation measures are required to reduce or compensate for the impact this development will have on the species and habitat. 

The fact that bats are nocturnal creatures means that public/street lighting can have a big impact on their environment.  EDC’s mitigation measures related to the site/public lighting on a recent project show how careful consideration of lighting design can help mitigate the impact that these local animal populations (in this case bats). 

 The following measures were taken from the Eurobats Guidelines for Consideration of Bats in Lighting projects to limit the impact of public lighting design on the local bat population: 

1. Eliminating U.V light

 EDC’s lighting design is solely using warm LED lighting which contains zero U.V light (which bats are particularly sensitive to). All new street lighting would be done in LED lighting so although this would be standard, it is a positive for the local bat population. The UV content of light is important in determining how attractive lamps are to insects (which are bats’ primary source of food). Bats feeding on insects close to street lights make them vulnerable to predators.

Figure – Table 1.1 from Eurobats Guidelines for Consideration of Bats in Lighting Projects

2. Warm White Light 

EDC used 2700K lamps throughout the entire development to minimize the amount of disruptive blue/UV light to which insects are attracted to. The Eurobats Guidelines for Consideration of Bats in Lighting Projects recommends the use of warm white lamps (with peak wavelengths above 580nm) with a correlated colour of >2700K. 

Figure – Table 5.1 from Eurobats Guidelines for Consideration of Bats in Lighting Projects


Figure – Variations in Lamp Peak Wavelengths

       3. Minimizing Light Spill/Trespass

      Nighttime light pollution is often exacerbated by poor lighting designs that emit light in upward directions and induce light trespass. This trespass may impact significant amounts of natural and semi-natural vegetation patches. Reducing light trespass may effectively limit impacts of light pollution on biodiversity.  

      EDC proposed to minimize upwards light spill with luminaires which provide no up-light. The proposed light fittings (Cree TRSA and the Cree Modern E) have a 100% downward light output ratio.

Figure 4-Cree Energy Uno

Figure 5-Cree URBAN Modern E

4. Minimizing Lux Levels

EDC designed to light to the minimum required lux levels of Cork City Council and avoid over-lighting of areas through the use of optics designed specifically to light only the required area. Three variations of the Cree Energy Uno (TRSA-02-75/TRSA-02-150/TRSA-02-200)  are in use within the project each with a different optic demonstrating consideration being given to the area that’s being lit. 


       5. Lighting Controls

       Peak feeding time for bats (when they exit the roost to go foraging) generally occurs at dusk. Using Cork City dimming profile U16B (these profiles differ from council to council) in the southern walkway/dark sky is a dimming scheme which is specifically for park areas/greenways and bat conservation areas. Passive InfraRed (PIRs)(Sensors) may also form part of the design in the southern and northern walkways of the site to ensure the lights are dimmed down/off unless needed.  

Figure – Extract from Cork City Council Exterior Lighting Design Requirements

       6. Reducing Column Heights

      Reducing column height can significantly reduce the light pollution around tree’s/vegetation. Low level bollard lighting(1M) was used  for the northern walkway to reduce light pollution and maintain a dark sky area to minimize the lighting impact on bats.

Figure – Effect of Reducing Column Heights from Eurobats Guidelines for Consideration of Bats in Lighting Projects

What we can do about light to combat lighting pollution?

1) Adopt Dark Sky-sensitive lighting that involves:

• For external lighting  – shields at 45 degrees with lightbulbs set deep inside, allowing downward (unidirectional) lighting only;

• Look for warm white sources. Their light is less harsh and less harmful to human health and the environment.

• lower wattage bulbs, dimmers, timers and/or motion-sensors — along with focussing light downwards, this is how best to conserve energy.

2) Don’t forget we as humans can be affected by the effects of light. To minimize harm from blue light in your home, choose the right lightbulb and download a colour temperature app that adapts your electronic screen to the time of day — cool light during the day and warm light at night (see

Figure 9  light pollution, street lights and proper shielding.  LUMICAN –


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