Very, very dark.

As late as 400 years ago, say, the Earth would have looked very, very dark. There would be no "webs of light," hardly any glimmering dots to illuminate cities. Jane Brox, opens her book Brilliant: The Evolution of Artificial Light with the exact answer to your question:

"Five hundred years ago, if you could have seen the Earth from above, cities, towns, and villages would have appeared nearly as dark as the oak forests. Perhaps glints of light would have leaked through doorways and shuttered windows early in the evening, or a few lanterns would have bobbed down the lanes, but no streetlights would have shone. Within, candles and lamps no brighter than those of Roman times would have lit only a bowl of porridge, a book, a shirtsleeve in need of mending, another. If someone reached for a thread or let out a long sigh, the flame would quiver, and the shadows would quiver, too. Then everything would right itself again."

Until about 1600 or so, you would have looked down on a dark world. The brightest illumination on the dark side would have come from flashes of lightning and wildfires in the forested expanses of the globe. Perhaps a volcano might have dotted the scenery every few decades or few thousand miles.

The fact is, lighting technology is almost as old as mankind, but it remained expensive until relatively recently. The Lascaux Cave contained lamps dated to more than 15,000 BCE, but those lamps provided lighting through burning animal fat. That was in limited supply and hard to get.

Turn the fat into oil, combine it with a wick, and it lasts longer. Beeswax candles may have been developed in Roman times, but tallow candles were far more common — beeswax was simply too expensive and rare to use regularly.

There were plenty of alternatives, used around the world. Rushlights — rushes soaked in fat — were used in Europe. In the South Pacific, people skewered candlenuts on bamboo to make torches. Here in Alaska, we have the candlefish, known for its oil content — but seal and whale oil were even better. Pine knots — sometimes called candlewood — were burned along the Eastern seaboard of North America, even after colonization.

But these all were limited. Brox notes that in 1743, the president of Harvard University, the Rev. Edward Holyoke, made 78 pounds of candles on two days in May. Less than six months later, they were all gone.

There were ingenious ways to spread the light of candles and lamps — mirrors and water diffraction were favored tricks — but it wasn't until the 17th century that lighting started to grow.

First came the whalers, who were able to provide massive amounts of high-quality oil. Then came the gas lamps, which allowed for reliable street lighting on a large scale. The development of oil wells in the latter years of the 19th century brought even more lighting, but it was the widespread use of electricity and the development of the practical electric light that truly spread those "webs of light" that you mention.

If you want to read more, I suggest reading some of Brian Bowers' works. He's written extensively on lighting technology and his Lengthening the Day has been published by Oxford University Press.

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Now, you asked about light in your comment, but your original question was what the ancient world looked like from space. I think it's worthwhile to mention the other ways the world looks different today. First and foremost, let's talk about deforestation and reforestation.

Until the past half-century, wood was valued not only for burning and light (as mentioned above), but for construction — as a building material and a tool-making material. That has meant a massive amount of deforestation.

In the "ancient world," as you mention it in your question, forests towered over Germany and Poland. From the Mississippi River to the Atlantic Ocean was a titanic forest, almost unbroken by human activity.

By 1900, that had almost all gone, the result of human activity. Look at Earth during the "ancient world" and you'd see giant unbroken expanses of green. Look at the world again in 1900, and you'd see those forests replaced by grasslands and farming fields. And yet, over the past 100 years, we've seen huge growth in forests.

With less need for wood as a heating fuel or construction material — not to mention huge tracts set aside for preservation — forests are rebounding. Not everywhere, mind you — in poorer countries especially, deforestation is proceeding rapidly — but in the developed world, the amount of forested land has grown.

That expanse of forest, not just lighting, would be one of the biggest differences between the Earth of the "ancient world" and the Earth of today.