Light exposure in digital cameras refers to the amount of light that enters through the lens. Light is what is needed to create or develop a photograph. Exposure refers to a shutter cycle or the amount of time the shutter is open to allow light to reach the sensor in a digital camera. A long exposure is when the shutter is open for a longer period of time to allow more light to enter. It is used a low light setting such as dusk or nighttime.
A picture is overexposed when the highlights of the photo are “blown out” or almost all white. An underexposed photograph is missing detail in the shadows. The shadow areas may be dark or black and hard to distinguish different features. As a photographer you can intentionally over- or under- expose a photograph for the artistic effect. An over- or under- exposed photograph is not necessarily a ruined shot.
When using manual mode on your digital camera, you can adjust the aperture and shutter speed to get the desired level of exposure. Opening the aperture increases exposure while it decreases depth of field. A slower shutter speed increases exposure, the amount of light, but also increases the chance of motion blur.
The exposure you want for a picture is determined by the subject and available light. In film photography the sensitivity is known as ISO. Fast film requires less light and has a higher ISO value. Exposure is the length of time the shutter is open and the level of light received onto the film or digital sensor. You can control the exposure by controlling shutter speed and the amount of light coming in from your aperture size. For the greatest amount of exposure, or light, you need a slow shutter speed and a larger aperture size.