Bats are nocturnal which makes them sensitive to artificial lighting. Inappropriate lighting can increase predation on bats, prevent them from feeding, commuting or getting in and out of their roost.
If bats are present you should get ecological advice and consult a lighting engineer in the early planning stages. More detailed information is available from The Bat Conservation Trust artificial lighting guidance.
The ecologist will need to provide:
- identification of key habitats / roosts
- recommended buffer zones and widths
- species-appropriate lux limits (0 - 1 lux)
- seasonal or time-based variations
- requests for vertical, elevated horizontal or upward calculation planes (lux contour plans)
The lighting engineer will need to provide:
- lux contour plans including those specified by ecologist
- luminaire and complete lighting specification, number, model, output settings, maintenance factor
- details of assumptions and conditions for example, duration, timers,
internal lighting, curtains - an explanatory note including potential glare sources and mitigation
Mitigating the effect of development
You can mitigate the effect of development on bats by including dark buffers, illuminance limits, zonation, appropriate luminaires, sensitive site design, screening, glazing treatments, creation of alternative habitats and dimming.
Mitigation options should be recommended by the lighting engineer and the ecologist
Key lighting specifications
Lighting suitable for bats should have:
- LED
- warm white spectrum < 2700 Kelvin
- a dimmable light, with motion sensors (PIR) and short timers
- 0% upward light ratio
- careful consideration of position and height
- recessed internal lights
- screening (planting, hardscape, hoods or cowls)