Mirrors show you the image of whatever you set in front of them. If you stand in front of the mirror and raise your hand, an image of a person raising his hand appears. Light, however, works differently when it hits a mirror, thanks to the Law of Conservation of Energy. Light is actually energy, and because energy can't be created or destroyed, it has to go somewhere when it hits the surface of the mirror. Rather than passing through, it bounces back out at an angle and continues into the rest of the room. Using multiple mirrors, however, you can reflect light and create an interesting effect, especially in dark rooms with bright, colored lights. Once you understand the basic concept, you can use mirrors and light to create brighter, more open rooms.
Account for the angle of reflection. Light bounces back out at the same angle that it hits the mirror. Knowing where the light is going to go will allow you to place the next mirror in such a way that it reflects the same beam.
Set up your mirrors. Place them facing each other and close enough that the light doesn't fade between each one. This will depend on the strength of the light you use--the stronger the better if you're looking for a dramatic effect.
Check your angles. Start by shining a single light at your first mirror. Watch how the light bounces off, and be sure that it hits the mirror across and slightly over from the first mirror. The light, when the mirrors are placed properly, should create a series of triangles. This is basic mirror-light reflection.
Set up your lights in their proper places. Lights are more dependent on the architecture of your space--the fixtures and electric sockets--than the mirrors are, so the placement of the lights is more important.
Track the angle of the light and then determine where you want the light to be. Imagine the original direction of the light as one side of a triangle. Once you've reached the end of that side, use a mirror to create the point from which the second side will emerge.
Hold up your mirror with the light on to be sure that it reflects the light the way you want. Once it does, mount it in place. You are now able to use a mirror to reflect light.
Direct beams of light work best for reflection with mirrors. Lights that disperse their energy--like lightbulbs, for example--tend to use that energy in the air before they reach the mirror, unless they're very close to the surface.