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