Generally, {HEAD ~ the optical elements} used in {TAIL ~ these lighting modules} are reflective or refractive elements 
used in
Generally , { HEAD ~ the optical elements } used in { TAIL ~ these lighting modules } are reflective or refractive elements
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH