Action: Use red lighting rather than other lighting colours
Key messagesRead our guidance on Key messages before continuing
- Two studies evaluated the effects of red lighting on bat populations. One study was in the UK and one study was in the Netherlands.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Abundance (1 study): One replicated, controlled, site comparison study in the Netherlands found that red lighting resulted in higher activity (relative abundance) for one of three bat species groups than white or green lighting.
USAGE (1 STUDY)
- Behaviour (1 study): One replicated, controlled study in the UK found that more soprano pipistrelles emerged from a roost when lit with red light than when lit with white light, but no difference was found between red and blue lights.
Red lighting may have a reduced effect on bats compared to lighting of other colours, as bat vision is more sensitive to shorter wavelengths (blue and ultraviolet light) than longer wavelengths (red light) (Müller et al 2009). For similar interventions, see ‘Use ‘warm white’ rather than ‘cool’ LED lights’ and ‘Use UV filters on lights’.
Müller B., Glösmann M., Peichl L., Knop G.C., Hagemann C. & Ammermüller J. (2009) Bat eyes have ultraviolet-sensitive cone photoreceptors. PLOS ONE, 4, e6390.
Supporting evidence from individual studies
A replicated, controlled study in 2000 at two bat roosts within buildings in Aberdeenshire, UK (Downs et al 2003) found that when roosts were illuminated with red light more soprano pipistrelles Pipistrellus pygmaeus emerged than when roosts were illuminated with white light, but no difference was found between red and blue lights. At both roosts, significantly more bats emerged when the roost entrance was illuminated with red light (13 and 72 bats) than when it was illuminated with white light (2 and 24 bats). No difference was found between red and blue light (6 and 62 bats emerging) at either roost. A hand-held halogen light with coloured filters was placed within 3–5 m of each of the two roosts. Over 20 nights in July–August 2000, nights with roosts unlit and nights with lighting were alternated. On nights with lighting, white, blue and red lights were rotated in a random order and changed every 30 seconds. On each of 20 nights, the number of bats emerging per 30 second interval was counted at dusk.
A replicated, controlled, site comparison study in 2012–2016 at eight forest sites in the Netherlands (Spoelstra et al 2017) found that red lighting had higher activity for one of three bat species groups than white or green lighting, and similar activity was recorded for all three species groups in red lighting and darkness. For Myotis and Plecotus spp. more bat passes were recorded in red light (66) and darkness (67) than in white (31) and green light (22). For Pipistrellus spp. fewer bat passes were recorded in red light (5,940) and darkness (3,655) than in white (17,157) and green light (9,695). None of the light treatments had a significant effect on the number of bat passes recorded for Nyctalus or Eptesicus spp. (red light: 495; white light: 719; green light: 950; dark: 521). At each of eight sites, one 100 m transect was set up for each of four treatments (red light, white light, green light or left dark). Five 4 m high light posts were installed along each transect. Lights (8 lux) were turned on from sunset to sunrise. Bat detectors recorded bat activity for 5–15 nights/transect in June–July and August–September in each year between 2012 and 2016.
- Downs N.C., Beaton V., Guest J., Polanski J., Robinson S.L. & Racey P.A. (2003) The effects of illuminating the roost entrance on the emergence behaviour of Pipistrellus pygmaeus. Biological Conservation, 111, 247-252
- Spoelstra K., van Grunsven R.H.A., Ramakers J.J.C., Ferguson K.B., Raap T., Donners M. & Veenendaal E.M. (2017) Response of bats to light with different spectra: light-shy and agile bat presence is affected by white and green, but not red light. Proceedings of the Royal Society of London. Series B: Biological Sciences, 284