{HEAD ~ The light} detecting {TAIL ~ means} is capable of sending an active signal as a light point is received thereon 
detecting
{ HEAD ~ The light } detecting { TAIL ~ means } is capable of sending an active signal as a light point is received thereon
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH