Figure 20: Spectral characteristics of silicon, the sun, and the human visual system. UV = ultraviolet and IR = infra-red.
The high sensitivity of silicon in the infra-red means that, for applications where a CCD (or other silicon-based) camera is to be used as a source of images for digital image processing and analysis, consideration should be given to using an IR blocking filter. This filter blocks wavelengths above 750 nm. and thus prevents "fogging" of the image from the longer wavelengths found in sunlight. Alternatively, a CCD-based camera can make an excellent sensor for the near infrared wavelength range of 750 nm to 1000 nm.