Shining a light on…light! – Different light types and their impacts.

Through reading my previous blogs you’ve now probably got a pretty good idea of how amazing and important bats are. Over the next few weeks, I’ll be going into a bit more detail about exactly how light impacts bats, so you know what to look out for when fighting light pollution! Today I’ll be briefly covering how various types of light affect bats in different ways.

First of all, it’s important to understand how light types differ from each other. Light travels in waves of different lengths and frequencies. The electromagnetic spectrum is a range of all these waves, most of which we can’t see. The wavelengths between 380-780 nm (nanometres) can been seen by humans and are known as ‘visible light’ [1]. Each colour we see has a specific wavelength which falls within this boundary. Most other plants and animals, including insects and snakes, can detect light outside of our spectral range, such as ultraviolet (UV) and infrared [2].

Photo credit: Cole-Palmer

We use a variety of light types which emit different wavelengths as a result of the materials used in the lamps [2]. Those which emit large amounts of invisible light are considered inefficient, as lots of energy is being wasted meaning more is required to achieve the brightness we want. As well as wasting energy, UV-emitting lights can attract animals which see it, causing many of them, largely insects, to cluster at a light source. Another issue is the colour ‘temperature’ of the light, as bats have been shown to be more sensitive to ‘cool’ blue lights [3]. The temperature of a light is measured in degrees Kelvin (K), with ratings below 3200 K considered to be ‘warm’ and those above 4000 k considered ‘cool’, which attracts insects [1, 4].

Photo credit: Power Outage Lights

So, what does this mean for bats?

As they eat insects, clusters at a light source will also attract light-tolerant bats, such as pipistrelles. This means they will have a competitive advantage over light-sensitive species, such as the Daubenton’s bat (Myotis daubentonii), which avoid the area. UV lights can also damage bats’ eyes, meaning over time they will struggle with navigation [3]. This is particularly worrying as some bats can live up to 30 years!

We’re all becoming a lot more aware of climate change, meaning many lights, both in our homes and on streets, are changing to become more efficient through emitting more visible light. This means the spectral composition and temperature of them are changing. For example, incandescent lamps were traditionally used for domestic lighting, although they are ‘warm’, they are being phased out as they emit lots of invisible infrared light [2]. Compact Fluorescent Lamps (CFL), Light Emitting-Diodes (LED) and Halogen lamps are replacing incandescent lamps [5]. However, CFLs and Halogen lights both emit UV, which if located outside or spill out of your windows, can negatively impact bats [6]. All three lamps are available in different colour temperatures, meaning those which emit ‘cool’ light can also impact bats.

Which lighting should you choose for your home?

It’s important you choose a light which doesn’t emit UV or ‘cool’ light. This is particularly important for any lights used outside for security or in the garden, as they contrast more with the night sky. LEDs are really efficient and are becoming increasingly popular, they don’t emit UV meaning they’re much more suitable than other modern lighting. Through using non-UV-emitting lights you can also save money as less energy is being put into making invisible light. However, if you don’t want to change your lights too much, UV-blocking glass and accessories are available for UV-emitting lights, to reduce how much spreads. Making sure you use a ‘warm’ bulb is also really important; these should be below 3200 K but ideally, to have minimal impact on bats, below 2700 K.

I hope I’ve helped you understand a bit more about how different lighting has different effects on both bat and other wildlife. It’s important to understand what the problem is so we know how to make changes which have a big impact!

Next week I’ll be going into more detail about how light affects the foraging behaviour of bats!

You can access information on this issue and find out how to help by following Blinded by the Night’s Facebook and Instagram pages. If you have any questions about the campaign or would like to get involved, please contact me via email at Beth2.Gerrard@live.uwe.ac.uk.

How to get involved:

Facebook: Blinded by the Night @blindedbythenightbristol

Instagram: @blindedbythenight_bats

References:

  1. URL: https://cdn.bats.org.uk/pdf/Bats_and_Lighting_-_Overview_of_evidence_and_mitigation_-_2014_UPDATE.pdf
  2. URL: https://link.springer.com/chapter/10.1007/978-3-319-25220-9_7
  3. URL: https://royalsocietypublishing.org/doi/full/10.1098/rspb.2017.0075
  4. URL: https://www.researchgate.net/publication/272889669_Impacts_of_artificial_lighting_on_bats_A_review_of_challenges_and_solutions
  5. URL: https://cdn.bats.org.uk/pdf/Resources/EUROBATSguidelines8_lightpollution.pdf?mtime=20181113114256&focal=none
  6. URL: https://ec.europa.eu/health/scientific_committees/opinions_layman/artificial-light/en/l-3/1-concerns.htm#0p0