The direction of the light source is revealed to us not only by the shadows it casts, but by the reflection of the light as well. Because light travels in straight lines, it always reflects off a surface at the same angle at which it strikes it.

In other words, the angle of incidence equals the angle of reflectance. It's a law of physics, and it's important, because it allow us to predict the directional effects of light.

For instance, we know that light rays striking a surface from the right will be reflected to the left. Light coming from above and behind the subject will be reflected up and to the front, sometimes directly into the lens of our camera. Of course, it's not always easy to see this Angle of Incidence Law at work.

The grass in this meadow, for instance, is made up of an infinite number of tiny surfaces, each presenting a different angle to the single angle of the sunlight striking it. And what's happening is the rays of light reflecting off the meadow are no longer organized in one straight line, but scattered in as many different angles of reflectance as there were angles of incidence. That's why we can't really "see" the concentrated reflection of the sun in the grass.

But sunlight can be almost blinding when reflected off a flat, smooth or shiny surface like a pool of still water, or the wing of an airplane, because there's a single angle of reflectance. The beam of reflected light reaches our eye or our camera concentrated and nearly intact. Of course, we can control the amount and quality of light reflecting directly from the subject to the camera by changing the relative positions of the camera, light source and/or subject.

So far we've learned how more or less solid objects reflect light coming directly from a single source; the sun. But shadows that are not lit directly by the sun still have light. It's called ambient light, and you'll find it, to a greater or lesser degree, anywhere you find direct light. Ambient light is any light which does not come directly from the primary light source. In fact, it has no direction quality at all. It's random light, reflected by the total environment around us - the ground, the sky, the walls of a room, even dust particles in the air. Ambient light pervades a lighting environment the way air tends to occupy a vacuum. It creates no obvious light or shade effects, and it keeps shadows from becoming totally black.

Let's see how we can manipulate the directional quality of light to convey different moods and different kinds of information about a subject.

When directional light strikes an object it defines that object's shape. How? By delineating three areas. A highlight appears as a very bright, small area on the subject because it reflects light directly into the eye or camera. Usually the reflected light is so bright that you can't see surface details in this area, and neither can your film. The lit area is bright and illuminated directly by the source, and you can see surface details. The shadow area is shaded from the light source by another part of the subject, and there is little or no detail. The combination of these three factors gives the viewer information about the shape, dimensions, texture and color of the subject. The shadow and lit areas and the boundary between them show us the object's shape. The lit area shows the subject's color. Texture appears at the edges of the lit area where light strikes surface irregularities. When we change the direction of the light either by moving the light source, changing the camera position, or reorienting the subject to the light source, things begin to happen.

The angles we choose depend on where we want the highlight, lit and shadow areas to be, and on what type of information we want to convey. And, of course, a great deal depends on the type of subject and the overall mood or feeling we want to achieve. The possibilities are almost limitless.