Mirrors and Light

[markalloyd]

If you put a mirror in a room and shine a light atthe mirror, is the amount of light in the room doubled? If so, does this not contradict the Law of Conservation of Energy? If not, er, why not?

[Rev. Green]

Light from a lamp will usually be absorbed by a wall. When light is reflected from a mirror it travels further before striking a surface which will absorb it. So there will be more light in the room at any particular time. Conservation of Energy is not affected: all the light is eventually absorbed.