" 'To know the dark, go dark,' advises Wendell Berry. But seen from satellites at night, our planet's continents burn as though on fire. Across the globe the collected glow from streetlights, parking lots, gas stations, shopping centers, sports stadiums, office buildings, and individual houses clearly details borders between land and water, sometimes spreading even into the sea on squid fishing boats, their spotlights built to mimic noonday sun. It would be one thing if all this light were beneficial. But while some does good work — guiding our way, offering a sense of security, adding beauty to our nightscape — most is waste. The light we see in photos from space, from an airplane window, from our fourteenth-floor hotel room, is light allowed to shine into the sky, into our eyes, illuminating little of what it was meant to, and costing us dearly. In ways we have long understood, in others we are just beginning to understand, night's natural darkness has always been invaluable for our health and the health of the natural world, and every living creature suffers from its loss.

"Our light-saturated age makes it difficult to imagine a time when night was actually dark, but not all that long ago it was. Until well into the twentieth century, what passed for outdoor lighting was simply one form or another of fire — torches, candles, or dim, stinking, unreliable lamps. And while these forms of lighting were an improvement on the earliest (skewering and burning oily fish or birds, gluing fireflies to your toes), how feeble this light was: A single 75-watt incandescent bulb burns one hundred times brighter than a candle. Historian E. Roger Ekirch reports that 'pre-modern observers spoke sarcastically of candles that made "darkness visible," ' and a French proverb advised, 'By candle-light a goat is lady-like.' Travelers considered moonlight to be the safest option for nighttime navigation, and lunar phases were watched far more closely than they are today. By the end of the seventeenth century, many European cities had some rudimentary form of public lighting, but not until the end of the nineteenth century did any system of electric lights — now so easily taken for granted — come into use. The darkness of our nights has been fading steadily ever since.

"No continents burn brighter than North America and Europe. Already, some two-thirds of Americans and Europeans no longer experience real night — that is, real darkness — and nearly all of us live in areas considered polluted by light. In the United States, Henry Beston's warning of 'lights and ever more lights' from Cape Cod in 1928 may have seemed extreme for many of the 120 million Americans alive at the time, most of whom lived in rural areas without electricity, but fewer than ten years later he was well on his way to being proven right. With FDR's signing into existence the Rural Electrification Administration in 1935, the old geography of night in the United States was certain to change. By the mid-1950s, whether in the city, the suburb, or the country, most Americans lived with electric light. In the half-century since, as the American population has risen past 300 million, those lights have continued their steady spread unabated and, for the most part, unnoticed. Could we jump from the dark of the 1930s (or 1950s, or even 1970s) to that of tonight, few of us would fail to be impressed by the dramatic increase in artificial light. But that increase has been gradual enough that it would be easy to imagine our nights are still as dark, or nearly so, as they ever were."