From experience we know that our pictures turn out well when a scene is brightly illuminated. Simply stated, light provides the energy necessary to record an image, so we need good lighting. Lousy lighting makes lousy pictures. Just as we find it hard to do good work when we feel low on energy, the camera has a hard time making a good picture without enough light energy. We need to make sure that the light comes together just right, or else the picture will still be lousy, even if the scene is sufficiently lit.
Another important consideration is the behavior of light. To design a camera that can form the best image possible, camera designers need to understand how light behaves as it propagates to the camera, through the camera, and finally onto the imaging sensor.