GENERATION, CONTROL, AND MEASUREMENT 189 



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3. CONTROL OF RADIANT ENERGY 



The following discussion pertains to the general properties of the more 

 common materials, optical components, and instruments used for con- 

 trolling the spectral composition and intensity of radiant flux. 



OPTICAL PROPERTIES OF MATERIALS 



Optical materials most generally used are (1) transparent substances 

 for lenses, prisms, diffusing screens, and windows; (2) reflecting materials 



