Chiaroscuro, as you remember, means light and dark. So it could be used of the light and dark of values; but, as a matter of fact, it is applied to the distribution of light and shadows, adopted by the artists of older times, and still used by many modern ones. In applying it, they represented the light, as coming from one direction, usually from behind their backs; and as striking the objects and figures in the picture at an angle, either on the right side or on the left. They also took care that the light should be concentrated or particularly bright at one spot. On the contrary, the artist who considers the light and dark of values, sees the light _in_ the scene he is painting, and observes that it pervades all parts of it.