Human visual system, spectral

Figure 4. The three-peaked spectral response of the human visual system, the peak...

A summary of symbols and units that are used in radiometry is shown in Table B.l. A summary of symbols and units that are used in photometry is shown in Table B.2. The photometric quantities use the same symbol except that the subscript v is added. A good introduction to the theory of radiometry is given by Poynton (2003), Jahne (2002), Horn (1986), and Levi (1993). See also International Commission on Illumination (1983). The radiometric units refer to physical quantities whereas the photometric units refer to perceptual quantities. In photometry, the physical quantities are weighted by the spectral sensitivity of the human visual system. Let Q(X) be the energy at wavelength X. Then, the corresponding photometric quantity is given by... 

In the human visual system, the JC f and Z tristimulus values are calculated from spectral power as given in the following equations (CIE, 1986). 

As the spectral sensitivity of the human visual system depends noticeably on the scene brightness, it is advisable to use the scotopic luminosity function V X) for night driving scenarios. 

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