A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light. The most familiar type of mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image.
Wendy had a pocket mirror that Batman borrowed while they were in the Justice League think tank. Batman used it to demonstrate how Superman could take a giant reflector up into outer space, to turn the dark hemisphere of Earth into day. Superman later flies over to Shamon's laboratory to borrow his reflector in his telescope, and used it to clear the dark side of the Earth from the Shamonite.