The facts of light
Most cameras work in much the same way; light reflected by objects enters through a lens onto an image sensor, which converts the light to digital values and creates an image. The amount of light hitting the sensor determines the quality of the image. If there is not enough incoming light, the sensor will not register an image at all.
The light sensitivity of a sensor is often expressed as a lux value. Lux is the unit for the amount of light falling on a given area. Camera manufacturers often specify a lux value as the operating minimum for their cameras. However, the advertised lux performance should not be the only point to be considered when evaluating a camera system. Many other factors come into play in low light conditions.
When the light level drops too low, the weak signal from the sensor will be subject to amplification, also known as gain. An unwanted side effect of amplifying the signal is that image noise is amplified, which in turn also increases the bandwidth and storage requirements.