Refractive elements generally cause {TAIL ~ the light} to change {HEAD ~ direction} and include lenses that can be used to focus or collimate light 
Refractive elements generally cause { TAIL ~ the light } to change { HEAD ~ direction } and include lenses that can be used to focus or collimate light
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH