With the development of science, many people began to realize such pollution as dust, gas, sewage and rubbish. But they only find out one aspect of the pollution. Many kinds of pollution are invisible, untouchable, and even more harmful. Light pollution is one of those kinds of pollution. Nowadays many mansions outside are decorated with mirror. Those mirrors can reflect 75 to 90 percent of the light reaching them. People staying in the light reflected from those mirrors will feel sick and uncomfortable. Those mirror walls also can lead to fire. Light pollution is very serious in cities.