Whether you are dealing with natural light or light coming from manmade sources, brightness or intensity is one of the most important considerations. The amount of light is not the same as the quality of light. Brightly lit situations — indoors or outdoors — are wonderful for shooting sharp, clear pictures because you can use slower film, smaller apertures, and faster shutter speeds. But once you have adjusted your aperture and shutter speed to match the brightness of the scene, the quality of the light becomes the most important factor in making a great image.
Dimly lit situations require faster film, larger apertures, and slower shutter speeds, which often result in grainy images that aren't as detailed as those taken in bright light. Scenes that are naturally low in contrast — a sand dollar on a pale sandy beach — may appear too washed out in flat lighting. If you don't want a washed-out look (that is, one with limited tonal range), you can add more light if you want to.
Naturally low-contrast scenes can be photographed without additional lighting, or you can increase the contrast by adding a strong light from any position that casts shadows that the camera will record. In most cases, you'll want a full tonal range from black to white, which means both brightly lit and shadowy areas in your pictures. You can use light in many different ways to create them. Regardless of the relative brightness of a scene, it will always be illuminated by two basic kinds of light. Each of these kinds of light can be effectively used to make different types of pictures, even different types of pictures of the same subject.