On cloudy nights, especially in winter, street lights of cities can illuminate large areas of surrounding countryside

Attending an evening carol service in a country church 5 miles from the outskirts of Milton Keynes, it seemed sensible to take a torch, envisaging tripping over the gravestones on the way back to the car park. However, it was entirely unnecessary. The light reflected off low clouds was so bright that it was easy to see the path.

With the UK weather recently featuring many nights of low cloud, the street lights of cities have been lighting large areas of surrounding countryside, an unlooked-for benefit of light pollution for pedestrians navigating their way home. Research shows that the reflected light is brightest within a city itself, often exceeding the light from a full moon. But measurements also show the effect can light up areas as far as 20 miles away – places considered on cloudless nights to be free of light pollution.