An imaging unit is arranged in {HEAD ~ front} of {TAIL ~ the photosensor array} such that it maps an image of said array of LEDs on said photosensor array 
An imaging unit is arranged in { HEAD ~ front } of { TAIL ~ the photosensor array } such that it maps an image of said array of LEDs on said photosensor array
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH