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