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