Photometric quantities

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 optoelectronic applications, photometric quantities are often used to express the degree of the current conversion into light. The luminous efficiency with the Lambertian emission pattern is... 

The various terms that are used for the description of the emission of electromagnetic radiation from a radiant source or for the receipt of electromagnetic radiation by a specified surface element are summarized in Tab. 3-9. The terminology of electromagnetic radiation measurement is divided into radiometry and the subset of photometry (Fig. 3-18). The former is the science that involves the energy measurement of electromagnetic radiation in general. The latter is applied for the same purpose when visible radiation is to be described or measured in relation to the human eye s response. Important photometric quantities are for example luminous flux, luminous intensity, illuminance and luminance (McCluney, 1994). Every photometric quantity has its counterpart in radiometry, and vice versa. 

Units, Symbols, and Equations for Radiometric and Photometric Quantities 77 Ed. Removed (this information is contained in 90 Ed., p. 2-1 and 2-29)... 

UNITS, SYMBOLS, AND EQUATIONS FOR RADIOMETRIC AND PHOTOMETRIC QUANTITIES... 

Note The symbols for photometric quantities (see following table) are the same as those for the corresponding radiometric quantities (see above). When it is necessary to differentiate them the subscripts r and e respectively should be used. e.g.. Q, and Q,. 

Units, Symbols, and Equations for Radiometric and Photometric Quantities... 

In addition to these two radiometric assessments of the beam intensity, for beams of visible light there is a third possibility, which is to quantify the intensity of the beam by the intensity of visual perception by the human eye. Physical quantities connected with this physiological type of assessment are called photometric quantities, in contrast to the two radiometric quantities described above. In photometry, the intensity of the beam is called the luminous intensity 7y. The subscript v stands for visual . The luminous intensity 7v is an ISO recommended base quantity the corresponding SI base unit is the candela (cd). The luminous flux is determined as the product of the luminous intensity and the solid angle. Its dimensions therefore are luminous intensity times solid angle, so that the SI unit of the luminous flux < v turns out to be candela times steradian (cd sr). A derived unit, the lumen (Im), such that 1 Im = 1 cd sr, has been introduced for this product. 

Table 1.2-3 summarizes the names, definitions, and SI units for the most frequently used radiometric and photometric quantities in radiation physics. 

Table1.2-3 Radiometric and photometric quantities in radiation physics...

All these phenomena can be utilized in chemical sensors. Before discussing them, some photometric quantities must be defined. 

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