Mirrors will give an illusion that your room appears larger and brighter without even adding any actual space. the reflective surface can lighten and enlarge any room.
The trick is to extend the mirrored surface either to the adjacent perpendicular wall or ceiling surface, or incorporate a large enough mired surface to give the illusion of a larger room. Your room will feel more spacious with a wall-to-wall mirror but you can opt for hanging mirror to fit your theme or period feel of the room.
Mirrors can also help brighten a dark wall by reflecting the lighter side of the room. Mirrors are simple, yet very effective.