The device includes a first subset of light modulators and {HEAD ~ a second subset} of {TAIL ~ light modulators} 
The device includes a first subset of light modulators and { HEAD ~ a second subset } of { TAIL ~ light modulators }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL