When the light source is illuminated, however, {HEAD ~ the viewer} sees {TAIL ~ a complete image} on the exterior surface  
sees
When the light source is illuminated , however , { HEAD ~ the viewer } sees { TAIL ~ a complete image } on the exterior surface
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH