Posted by Ellery McNaughton @EJ_McNaughton

Dear Batman,

I have a bone to pick with you. Maybe you’ve been too busy fighting crime and/or Superman to notice that sky glow from artificial light sources is a global issue. Light emitted upwards from artificial sources is scattered by molecules in the atmosphere, creating a glow that is brighter than the natural night sky. Aside from making it harder to sneak around in your Bat-Plane, sky glow also reduces star visibility (and therefore sights like these), and has a myriad of potential impacts on the environment. It is for this reason that I find your use of the Bat-Signal downright irresponsible.

The Bat-Signal, a symbol of hope, fear, and excessive light pollution

You see Batman, when it comes to outdoor lighting there are three main ways to reduce sky glow. The first is to reduce light trespass into the night sky by shielding or directing the light source downwards. The second is to reduce the amount of light emitting into the night sky by dimming or switching off the light source. The third way is to reduce the scattering of light in the night sky by avoiding light sources that emit strongly in the blue part of the spectrum (as short wavelengths scatter more). Ideally these three methods should be used together. Props to you for somewhat shielding your light with a bat symbol, but I can’t help but feel that this is due to aesthetics, rather than good lighting practice.

While we’re at it, does Wayne Manor really need that much outdoor lighting?

In short, your Bat-Signal is polluting the night sky with its bright, upward emitting white light. Don’t take my word for it, go ahead and measure Gotham’s sky glow for yourself. I use a Sky Quality Meter (Unihedron) for my research, but there are also various apps you can easily access and use with your Bat-phone (e.g. Dark Sky Meter or Loss of the Night). You can test for yourself the variations in sky glow around your city, and help out with citizen science while you’re at it!

Honestly Batman, you’re known as the Dark Knight. Please at least try to live up to that.

Ellery McNaughton is a PhD student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. Her project will investigate the effects of a city-wide changeover in streetlight technology on urban bird behaviour and ecosystem function. She is supervised by Margaret Stanley, Jacqueline Beggs, Kevin Gaston (University of Exeter, UK) and Daryl Jones (Griffith University, Australia).