Darkness is just the absence of photons. Or is it?

A National Heritage is something special. Whether it’s a work of art or a natural wonder, it’s something unique that people are proud of. It’s a part of the culture of the place; something to preserve, protect, and enjoy.

There are many different kinds of National Heritage, but the Australian state of New South Wales has one a bit more different than the rest.

It’s the night sky.

Look outside on a balcony, late in the evening, soon after the Sun has gone down for the night. As darkness follows it across the sky, chances are, you will see many small white lights dotting the horizon. Some are bright, and some are dimmer, but they all come up every night without fail.

Over time, you may become familiar with the lights, and see the different patterns they make. Some are far apart so you can make out individual points, while others merge together in one bright blur.

Those are street-lights.

“When I was a little kid,” said tech entrepreneur Elon Musk, “I was really scared of the dark. But then I came to understand, dark just means the absence of photons in the visible wavelength — 400 to 700 nanometers. Then I thought, well, it’s really silly to be afraid of a lack of photons. Then I wasn’t afraid of the dark anymore after that.”

As it turns out, there is a good reason to be scared of lack of photons. Photons are light. They bounce off objects and into your eyes, and that helps you make out what’s in front of you. Lack of them can be dangerous, especially if you’re in some new, unfamiliar place, where anything may come out at you, at any moment.

People aren’t scared of the dark. They’re scared of what’s inside it.

Earlier, darkness couldn’t be helped. When night-time came, people would stay home without venturing outside. They might gather around a bonfire, and eventually go to sleep.

Then came candles, which helped them move about a bit further, and oil-lamps, which helped them keep going a bit later into the night. But the real revolution came with the electric lightbulb.

Nowadays, people have lights on all the time. They have lights in the streets so they don’t bump into cars. They have lights in their homes so they don’t bump into chairs. They can see things wherever they want, whenever they want.

But all those lights also has a side-effect: light pollution.

Lights don’t just shine where people want to look. Some light also goes sideways along the ground and up into the sky. And when there are many lights together, like in a big town or city, they create a glow which can brighten up the whole night — making it difficult to see the stars and planets and everything else there is to see up there.

In January 1994, a 6.7-magnitude earthquake hit the community of Northridge in California, USA.

It was one of the worst natural disasters in the history of the country. Over sixty people died, and thousands more were injured. Forty-thousand people were left homeless, and the earthquake caused damages going up to tens of billions of dollars.

The timing was lucky, though. Most people were safe at home when the buildings collapsed, because it happened to strike on a national holiday. And, it was very early in the morning.

So early, in fact, that when people across the state woke with the trembling ground, and found that all the lights were out, thousands of them rushed out of their houses — and saw a clear night sky, unpolluted by light, for the first time in their lives.

That night, observatories and radio-stations were flooded with calls. People wanted to know about the sudden proliferation of stars, as well as the eerie silvery cloud that had appeared in the sky, and whether they perhaps had something to do with causing the earthquake.

The observatories replied that no, the stars were always there, it was just that they usually got drowned out by the city lights. And there was no need to worry about the “eerie white cloud”.

That, they explained, was just the Milky Way.

If people in 1994 had never seen the Milky Way, the situation today is even worse.

One in three can never see the Milky Way, because their skies are too bright. Over 80% of the world’s population is subjected to “skyglow”, the reddish-yellow glow that stays all through the night because of artificial light from below. They can never see an original night, the way our ancestors used to see it hundreds of years ago.

Amateur astronomer John Bortle came up with a scale to measure the darkness of skies. It starts with Class Nine, the “inner-city” sky, on past the city and suburbs at Five; down to the “rural sky” at Class Three with only “some indication of light polluting along the horizons”, and Class Two, a “truly dark site”.

But even a “truly dark site” is not the darkest you can get. Only the very lucky — or enterprising travellers — will ever see a sky of Bortle’s Class One: a sky so dark, the Milky Way casts visible shadows on the ground.

Chicken-farm chickens, incarcerated in small square wire-mesh cages, never get to see real daylight. Bright LEDs shine above their cage instead, alternating on and off every six hours. This creates an artificial twelve-hour “day” for the creatures, making them live faster, lay eggs faster, and grow fatter faster to be quickly killed and eaten.

Light pollution isn’t just about missing out on stars. There are effects here on Earth as well.

To start with, bright lights affect the sleep cycle. And today’s LEDs, with their bright blue lights, are even worse. They suppress the production of sleep-hormone melatonin, and generally keep your body in “daylight” mode. In cities, people have started staying up late and sleeping through the morning, in what sleep-researcher Steven Lockley calls a permanent “mini jetlag”.

Research is still in the early stages, but disruption of the body clock could have various medical consequences. These include depression, insomnia, heart-disease, and even a possible (though not yet proven) link to breast-cancer.

And some of the effects, according to studies on hamsters, can even be passed on genetically.

But it’s not just humans that are affected. If light pollution affects us, it affects other animals even more. Migrating birds lose their way in the sky. Frogs stop their mating calls when exposed to too much light. Baby turtles lose their way, mistaking electric lights for the moon-reflection of their ocean home. And night-time animals never find a good time to venture out at all.

The effects affect plants, too. Flowers don’t get pollinated because their moths get distracted. Soybeans fail to seed, because they’re forever waiting for the shorter days that signal “winter is coming”. Trees miss out on their equivalent of sleep, because they don’t know when to rest and when to photosynthesise. They can’t figure out what season it is, which is why too much light also makes them jump the gun and bring on springtime early.

The thing about light is, we don’t actually need so much of it. Light has become so cheap that people simply put them up and leave them on even if they’re not actually being used.

Every year, the world spends billions of dollars — on extra light that serves no purpose.

People also use lights that are much brighter than needed. Light researcher Christopher Kyba, of the German Research Centre for Geoscience, explains that humans see not by brightness but by contrast. If a light is just bright enough to see things by, there’s no point making it brighter. In fact, it may even be worse, because it’ll dazzle your eyes and make them unable to see things in darker spots.

If you’re driving at night, you’ll know that feeling. Look into an oncoming headlight, and you’ll become temporarily blind to everything else.

That means bright streetlights may actually make cities less safe, rather than more. They’ll just dazzle you so you won’t be able to see the shady character lurking in a darker alleyway — or in the best hiding-spot, right behind the bright lamp-post.

Finally, there’s the issue of lighting much more than you actually need to. Lights are rarely shaded properly. A typical streetlight shines not just on the pavement, but also up into the sky, onto the lens of a now-dazzled CCTV camera, and in through the neighbour’s bedroom window.

Dark-sky advocated are pushing the concept of “light trespass”, which is when one person’s light shines into another person’s property. It’s a simple concept, but it could work wonders.

Light pollution is different from other kinds of pollution. It’s easy to undo, would save everyone a lot of energy if it went, and could be gone in an instant if everybody put in just a little bit of effort.

Shield your lights. Keep them dim. Switch off when not in use. Avoid the blue. And that’s really all there is to it!

There are movements like the International Dark Sky Association and Globe at Night, which hope to bring back the night some day. Local governments around the world have already begun passing laws to keep light-pollution down, and Dark Sky Parks have been set up where all but the dimmest lights are banned. There is, however, still a long way to go.

Meanwhile, thank goodness for power cuts!

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