Have you ever seen a lamp for a house's entry in a style called a "carriage lamp"? It's usually a tall rectangle of glass panes in a metal framework, with some sort of pendant shape underneath to balance the pointed top.

If you look at photos of surviving carriages, or period art, you will see carriage lamps sticking out of the sides of carriages, high and at the front. These oil lamps were lit at night both to illuminate the road in front of the horses and to let others see there was a carriage.

(Oil lamps are older than metal usage. There was no time of carriages before oil lamps.)

The driver often had handy a bull's eye lantern, flat bottomed with a carry ring on top, with a lens that concentrated the light to look at problems better, farther away. He usually had an assistant who could be sent out with the bull's-eye to look ahead of the stopped carriage to see if, say, the bridge were out.

Now, you may be thinking that an oil lamp doesn't throw light all that far. Not by modern standards of headlights. You also need to remember that, with regular changes of horses, the British fast stages averaged only 10mph through the night. The driver of any particular stage knew the road very well, from driving it every day or two.

Private carriages generally travelled more slowly to spare the horses. They usually didn't travel through the night on long trips, but of course you had to get home in the dark after a ball or dinner party.

So there wasn't much chance of over-driving the lights.

Of course, in towns, there might be street lights, or every third building required to hang a lantern above the door. Sometimes every building. It depended on where you were. So that illuminated the road.

If you are thinking Middle Ages, before glass was cheap - well, coaches are a Renaissance development, invented in Hungary. They had glass lanterns by then. Also, the early coaches were expensive, and rare. So their owners could afford good lanterns. The roads weren't full of them.

What people forget is that without good roads, wheeled travel is a penance, not a pleasure. So in most times and places, people prefer a saddle to a coach. At the least, you want some smoothed gravel, not a mess of rutted hard dirt or gooey mud try to roll through. This also keeps down the speed of travel, way down. Those speeds I gave you? Based on the great age of coaching, with Telford and Macadam roads (both of them improved gravel).

Arnold, All Drawn by Horses. (all sorts of vehicles)

Badminton Sports Library, Driving (chapters that are all reminiscences of mail coach drivers, or a dictionary of carriage types, or how to drive tandem)

Smiles, The Life of Thomas Telford which discusses the roads of England before Telford roads, which outside of towns were hellish to non-existent, for the most part)

Ohler, The Medieval Traveller (nope, no coaches)

Piggott, Chariot, Waggon, Coach (historical development, ending with a coach of Elizabeth I)