The shift to LED lighting is stopping us from seeing our night skies

A story I like to tell from my childhood, to help people understand the importance of dark night skies, is about growing up in Los Angeles next to a freeway. I am a child of the smoggy 1980s and 1990s in LA, when the air quality was infamously bad. The city was also incredibly lit-up at night. The smog and light pollution created a situation where we could see almost no celestial features except for the moon and sometimes Venus.

I didn’t see a dark night sky until I was a teenager, when I learned for the first time that, given the right conditions, we can see the Milky Way with the naked eye. I had no idea.

Almost two decades later, while I was in Chile on my first and only professional telescope observing run, I stood under a clear southern sky and realised that my ancestors had seen skies like this all the time. They didn’t have to travel for 24 hours across thousands of miles. A dark night sky was their norm. This is how they evolved and how they lived every evening. I saw then how much us inner-city kids were denied by the bright lights and air pollution of our beloved hometowns. We were cut off from seeing the cosmos the way our ancestors had.

At the time I had this revelation, a prominent feature of many US cities was that night-time street lights were orange-ish. Many of these were sodium vapour lamps, which emit light at a characteristic frequency for sodium, 589 nanometres. This meant the light was around one wavelength, so was orange, giving cities a kind of fiery halo in the evenings.

The problem with sodium vapour lighting is that it is less energy efficient than newer technologies. Around the time I was in Chile, there was a big policy push to shift to LED lighting, which uses a lot less energy. It is a great idea. The only problem? The transformation to LED lighting, which was advanced by policy-makers across the US, didn’t come with a requirement that the light be filtered to only a single frequency, the way sodium lights work. As a result, a lot of the lighting installed around the country is now white light.

White light is a composition of many different frequencies, and it mimics sunlight. Animals (including humans) have different biological responses to white light compared with orange light because we are programmed to interpret it as daylight, so it can disrupt circadian rhythms.

Light pollution can be a problem in any frequency, of course, especially when lighting isn’t focused on the place where it is needed: the ground, not the sky. Broad-spectrum LED lighting adds to these challenges when it isn’t carefully regulated.

I recently returned to my hometown to participate in the Los Angeles Times Festival of Books and was out late for a few nights due to the festivities. This was my first time going back since taking up amateur astronomy, so of course I looked up, to check the sky.

At around 10pm on my first night, I was shaken by what I saw. The horizon looked like the sun had just set. I knew something was different, but initially couldn’t figure out why it felt strange. Then I realised it was because the horizon was bright white, full of the glow of LED lighting, rather than the orange I grew up with. It also dawned on me with horror that I wouldn’t be seeing any stars while I was home. In effect, I relived the nearly-empty night sky of my childhood.

But this time it was different, because I could see in my mind exactly how much was missing. I also knew that it isn’t possible for amateur astronomers like my friend Marvin, who tells me he sees fewer stars today than five years ago, to easily filter out the light pollution, because it is now coming in every frequency.

Organisations like DarkSky International have documented the ways in which lighting can function as pollution, with impacts on everything from the very function of ecosystems to our ability to access our cultural night sky heritage. This might seem like a losing battle in metropolises like LA – which, like Randy Newman, I love – but luckily for us, that isn’t true. DarkSky International works actively with communities around the world to install responsible lighting that is safely focused on the ground, while also minimising negative impacts on communities. When we talk about being ecologically responsible, the way we illuminate our homes and streets at night has to be part of the conversation.

Want to help? Simple things you can do include installing blackout curtains in your home and making sure any outdoor lighting around your dwelling has shielding that focuses the light towards the ground. Educate yourself too, on the improvements your community can make to lighting – and then spread the knowledge, especially to decision-makers.

Chanda’s week

What I’m reading

Chicano Frankenstein by Daniel A. Olivas was so much fun.

What I’m watching

I really think the Coronation Street writers need to stop making Roy suffer so much!

What I’m working on

Thinking about a novel model of dark matter involving a different type of photon than normal.

Chanda Prescod-Weinstein is an associate professor of physics and astronomy, and a core faculty member in women’s studies at the University of New Hampshire. Her most recent book is The Disordered Cosmos: A journey into dark matter, spacetime, and dreams deferred