GENERATION, CONTROL, AND MEASUREMENT 



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the human eye. On this basis, "ultraviolet light," "infrared light," 

 "black light," and similar terms are misnomers that have no place in 

 precise scientific writing, although they may be useful in nontechnical 

 discussions. In place of the term "light" for the physical entity, it is 

 more consistent to use "radiant energy" or simply "energy." When 



Table 3-1. Comparison of Physical and Psychophysical 

 Kaoiant-energy Terms 



Prefixes: 



radi- pertaining to radiant energy 



photo- pertaining to luminous energy 

 but also applied to radiant 

 energy, as in "photograph" 

 and "photon" 



lumi- pertaining only to luminous en- 

 ergy 



irradi- concerning interception of radi- 

 ant flux 



illumi- concerning interception of lumi- 

 nous flux 



Suffixes: 



-ion process, as in "conduction" or 

 "calibration" 



-er, -or device, as in "generator" or 

 "absorber" 



-ance measurable property, as in "re- 

 sistance" or "reflectance" 



-ity specific property as in "den- 

 sity" or "conductivity" 



the concept of power is involved, "radiant flux" or "flux" is a suitable 

 term. Radiation implies the process of generation of radiant energy and 

 is not synonymous with radiant energy, although it is frequently so used, 

 especially by those dealing with ionizing radiant energy. "Radiant 

 emittance," "radiant intensity," and "radiance" are intensity terms 

 applicable to sources in that they are related to the radiant power per 

 unit area and/or solid angle. "Irradiance" is the intensity term appli- 

 cable to the interception of radiant energy by objects and is power per 

 unit area. Frequently "intensity" is used loosely as a substitute for 



