As interior design items, wall mirrors perform up to four functions: art objects, light enhancers, space amplifiers, and item multipliers.
A well-decorated room or a good view deserves to be seen more than once. A strategically placed mirror will reflect a portion of a room, an exquisite window view, or an exceptional piece of art. When you're framing a reflected view, be sure to choose a frame worthy of what the mirror reflects.
To know what the mirror will reflect, simply stand exactly where the mirror will be placed to see what the mirror will "see." Consider the height of the mirror, too. Mirrors placed high on a wall may reflect an abundance of ceiling. That can be a good thing if the room is small, but a potential problem in a high-ceilinged room. If that's the case, tilt the mirror slightly downward to improve the mirror's view.
One of the oldest "tricks" with mirrors is increasing candlepower -- literally! Think back to your days in history class: rooms from colonial times were candlelit, and the candles often had tin sconces to reflect the light. To make the light reflect even more, the tin was bent and folded to create more facets, thus more reflection.
Mirrors are still used to the same effect with candles or lamps. The key thing to remember is that a mirror reflection of a bulb can be blindingly bright; a well-chosen lamp shade will tone down bright bulbs, and low-wattage, frosted bulbs cast a softer light closer to candle-like intensity.
Mirrors work one of two ways to make a room look larger. An oversized mirror, or a wall covered in mirrors simply reflects the entire space of a room to make it look twice as large. It's a design trick popular in small dining rooms and baths.
Another, more subtle choice is to put a large mirror where a window could possibly be placed; it creates the impression of another room beyond. Mirrors used in this fashion often have a window-frame treatment to further enhance the illusion.
Anything placed close to a mirror appears to have twice the mass. A floral arrangement or coffee service placed in front of a mirror takes on a grander sense. To get the most effect, use a modest-sized mirror and place items as close to the mirror as possible. If the mirror is large and the item small, the effect is lost.
One thing sometimes forgotten is that items in front of a mirror can't have a "bad side." All sides are exposed, so choose items carefully. Conversely, items that look great on all sides can be fully enjoyed. Small Christmas trees, for example, laden with ornaments have extra sparkle when placed in front of a mirror.