Editing Spectroradiometer (section)

==Background==

The field of [[spectroradiometry]] concerns itself with the measurement of absolute radiometric quantities in narrow wavelength intervals.<ref>Leslie D. Stroebel and Richard D. Zakia (1993). Focal Encyclopedia of Photography (3rd ed. ed.). Focal Press. p. 115. {{ISBN|0-240-51417-3}}</ref> It is useful to sample the spectrum with narrow bandwidth and wavelength increments because many sources have line structures <ref>Berns, Roy S. "Precision and Accuracy Measurements." Billmeyer and Saltzman's Principles of Color Technology. 3rd ed. New York: John Wiley & Sons, 2000. 97-100. Print</ref> Most often in spectroradiometry, spectral irradiance is the desired measurement. In practice, the average spectral irradiance is measured, shown mathematically as the approximation:

: <math>E(\lambda)=\frac{\Delta\Phi}{\Delta A \Delta\lambda}</math>

Where <math>E</math> is the spectral irradiance, <math>\Phi</math> is the radiant flux of the source ([[SI]] unit: [[watt]], W) within a wavelength interval <math>\Delta\lambda </math> (SI unit: [[meter]], m), incident on the surface area, <math>A</math> (SI unit: square meter, m<sup>2</sup>). The SI unit for spectral irradiance is W/m<sup>3</sup>. However it is often more useful to measure area in terms of [[centimeters]] and wavelength in [[nanometers]], thus submultiples of the SI units of spectral irradiance will be used, for example μW/cm<sup>2</sup>*nm<ref name=Kostkowski/>

Spectral irradiance will vary from point to point on the surface in general. In practice, it is important note how radiant flux varies with direction, the size of the solid angle subtended by the source at each point on the surface, and the orientation of the surface. Given these considerations, it is often more prudent to use a more rigorous form of the equation to account for these dependencies<ref name=Kostkowski>Kostkowski, Henry J. Reliable Spectroradiometry. La Plata, MD: Spectroradiometry Consulting, 1997. Print.</ref>

Note that the prefix "spectral" is to be understood as an abbreviation of the phrase "spectral concentration of" which is understood and defined by the CIE as the "quotient of the radiometric quantity taken over an infinitesimal range on either side of a given wavelength, by the range".<ref>Sanders, Charles L., and R. Rotter. The Spectroradiometric Measurement of Light Sources. Paris, France: Bureau Central De La CIE, 1984. Print.</ref>