In some ways, photographers resemble musicians more than painters, sculptors, and other visual artists. This is because photographers, like musicians, are more interested in the manipulation of energy than that of matter.
Photography begins the moment light is emitted from a source. She is the manipulation of light. Whether the manipulations are physical, chemical, electrical, or electronic, they are all motivated by the same mission and guide by the same understanding of how light behaves.
The three most important qualities of any light source are its brightness, color and contrast. But the subject, not just the light, has a major influence on lighting. He can transmit, absorb,or reflect the light that strikes it.
Of the three ways the subject can affect the lighting, reflection is the most visible.
Light Science & Magic, an introduction to Photographic Lighting
