High contrast results from deep shadow and bright light in the same image. Brightness is the single most important quality of light. An abundance of light makes possible the use of smaller apertures , faster shutter speeds and slower film , all of which generally make for clearer photos. The lack of strong shadow indicates an overcast day, producing low contrast illumination, often the best lighting for portraiture.
Contrast is a function of the angle at which the light strikes a photographic subject.
Bright sun on a clear day will generally produce a high contrast situation with its pronounced shadows. Details disappear in both the opposing darkness and brightness. This light is suitable for compositions that are bold and graphic-oriented and generally unsuitable for emotional, moody images. Shadows are filled in and contours are less sharply defined. Very low contrast light can seem to come from everywhere, but nowhere in particular, and can result in dream-like images.