c) detecting {HEAD ~ light} of {TAIL ~ such wavelength} that is reflected or scattered by the sheet, and 
of
c ) detecting { HEAD ~ light } of { TAIL ~ such wavelength } that is reflected or scattered by the sheet , and
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH