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