Well, not being an interior decorator myself I can't say for certain what they actually use. But I can tell you how the mirrors work. You're right that concave mirrors focus the light together, so that more light can hit a single spot on your eye. However, more light hitting each spot on your eye does not mean that the object appears larger
- it means that the object appears brighter
Convex mirrors, on the other hand, work by bending light apart. Imagine two light rays - one coming from the top of an object and one from the bottom. If these two light rays are bent by a convex mirror, they will end up farther apart than they were before. This means that the object will look larger, just like you've heard:
A concave mirror can make something look smaller or larger depending on where the object is located. In order for the object to appear larger, though, it has to be at just the right position (between the mirror's focal point and its center of curvature)... However, this will also make the object appear to be upside down, an effect which most interior decorators probably aren't shooting for:
(For animations showing the object at other locations, check out the Shockwave Studios: Ray Optics
Hope this helps!
(republished on 07/28/06)