Look at North America from a satellite at night and it glows, with billions of wasted energy dollars.
Nobody meant this to happen, and it's having a devastating effect on our health.
It turns out we need the darkness to make our immune systems work.
Darkness for Health
Scientists have now discovered that only when it's really dark can your body produce the hormone called melatonin. Melatonin fights diseases, including breast and prostate cancer.
"It turns off the cancer cells from growing," says Joan Roberts, a photo biologist.
But if there's even a little light around your bed at night, your melatonin production switches off.
"So there may be this natural way that Mother Nature has given us, that is, dark night to keep certain cancers under control," Roberts says.
Even watching TV turns on other immune system hormones that should be active only in daytime. They get depleted, and you're more likely to get a cold.
Nature needs darkness, too.
The immune systems of animals grow weak if there's artificial light at night.
It turns out that's easy to fix. Lights that spill so much glare up into the sky that it even wipes out the stars can be shielded with reflectors to focus on the light and make them more efficient. Or, you can simply switch off the lights.
For example, by going dark at night, some office buildings and school systems are each now saving as much as $1 million a year.
At the Sears Tower in Chicago, they are turning out the lights to save the birds. Millions of migrating birds die every year when they are attracted to the lights and fly into the buildings.
And there's another surprise: Police report that such darkness is often safer. That's partly because neighbors soon learn to alert police if they see any lights on in a building. There's even less graffiti because it's usually lighted walls that attract the spray-can vandals, not dark ones.
Around Tucson, Ariz., the site of observatories and where law requires that lights focus down only on what needs to be lighted, people have even discovered the stars again. Some say they've also discovered how much we lost when we wiped out dark night and its natural promotion of safety and health.