[daveo]

I'm sure you already know that a mirror's purpose is to reflect. When you look into a mirror, you expect to see a reflection staring back at you. We rely on mirrors everyday when we drive, for personal care like brushing our hair or putting on make-up, and maybe even for looking in hard to see places.

But they can also help reduce your electric bill, if placed correctly.

Since mirrors reflect, if you position a light source correctly near a mirror, the mirror will reflect the light outward. This can in a way "emulate" a second light source without actually physically having another light there. (Think of it as a virtual light).

You can prove this to yourself. If you have a mirror, place it across from a decent light source, like a bigger lamp. Turn on the light. Play with the positioning of the mirror until the room "brightens." Of course, hacing lighter colored walls certainly helps the experiment, but even with darker walls, the difference is noticeable. The room seems brighter, since the mirror is simply reflecting the light. It's acting like a light source, even though it is not actually producing any light.