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.
Researchers trying to measure the effect of various cloud types on the intensity of light came to the conclusion that it hardly mattered: it was simply that the closer the cloud was to the ground, the greater the reflected light, both locally and at distance. They did discover that in winter, when then temperature drops to below freezing, even more light is reflected by ice crystals and scattered back on the ground below.
