Use red lighting rather than other lighting colours
Overall effectiveness category Likely to be beneficial
Number of studies: 3
Background information and definitions
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). However, a study in Latvia found that migratory bats may be attracted to red lighting, which could have negative consequences (Voigt et al. 2019).
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.
Voigt C.C., Rehnig K., Lindecke O. & Pētersons G. (2018) Migratory bats are attracted by red light but not by warm-white light: implications for the protection of nocturnal migrants. Ecology and Evolution, 8, 9353–9361.
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, 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.Study and other actions tested
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.Study and other actions tested
Referenced paperSpoelstra 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.
A site comparison study in 2015 of two road culverts near Elburg, Netherlands (Spoelstra et al 2018) found that culverts illuminated with red light had similar activity of commuting Daubenton’s bats Myotis daubentonii as culverts illuminated with green or white light. The average number of Daubenton’s bat passes did not differ significantly between culverts illuminated with red (43 bat passes/night), green (37 bat passes/night) or white light (39 bat passes/night). Activity was similar when culverts were left unlit (34 bat passes/night). Two light-emitting diode (LED) lamps of three colours (red, green, white) were installed on the ceiling of each of two identical, parallel road culverts (31 m long, 1.6 m diameter) carrying a stream. Different light treatments (unlit; red, green, or white light at 5 lux intensity) were applied simultaneously in each of the two culverts with treatments changed each night over a total of 47 nights in July–August 2015. Two bat detectors fitted alongside the lamps in each of the two culverts recorded bat activity.Study and other actions tested