The output surface is only partially reflective, thereby allowing a portion of the light to escape the wedge and provide the line of {HEAD ~ light} which illuminates {TAIL ~ the document} 
The output surface is only partially reflective , thereby allowing a portion of the light to escape the wedge and provide the line of { HEAD ~ light } which illuminates { TAIL ~ the document }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL