Low light solutions

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.

Figure 1: Reflected light is collected through a lens onto an image sensor, which converts the light to digital values and forms an image.

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.

Figure 2: The lux value varies according to lighting conditions. In the image to the left, the lux value measures 130 000 lux in direct sunlight, and 10 000 lux in the shaded areas. In the office environment, the lux value is only 50 lux. In the image to the right, the lux value is around 200 lux.

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.

Figure 3: Low gain = little noise, high gain = more noise. 

The right amount of light