The angle of incidence of the originating light beam with respect to the input surface of the beam directing member satisfies {HEAD ~ a predetermined relationship} between {TAIL ~ the thickness} or separation between the reflective layers, the index of refraction of the material between the reflective layers, and the effective thickness or diameter of the beam entering between the two reflective layers 
The angle of incidence of the originating light beam with respect to the input surface of the beam directing member satisfies { HEAD ~ a predetermined relationship } between { TAIL ~ the thickness } or separation between the reflective layers , the index of refraction of the material between the reflective layers , and the effective thickness or diameter of the beam entering between the two reflective layers
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