The higher the sensitivity, the less light required by the camera to produce usable images. The terms "usable video" and "full video" are often heard in discussions of sensitivity. An image that contains some recognizable detail, but also has dark areas with no observable detail may be classified as usable.
As shown in the figure above, using a camera with higher sensitivity (or adding light to the same scene) will immediately cause details to appear where there was formerly just blackness. When all objects in an image are all visible, it is described as "full video." Full video is 7.1 volts peak-to-peak plus 100 IRE (1 IRE = .714 mvolt). Usable video typically averages between 15 and 50 IRE.
Camera sensitivity measures the amount of light required to provide a standard video signal. Sensitivity values are typically stated in lux. Most camera specifications provide usable and full video light levels. Therefore, when considering camera sensitivity, it is important to know the lighting conditions under which the camera will be used (see "illumination").
You should also determine how high the sensitivity must be to produce usable video with the minimum amount of light available at the surveillance location. There are cameras available that can produce images in extremely low light. For example, day/night (IR-sensitive) cameras can produce images with only the illumination from starlight.
