{HEAD ~ The spacer} means is in operative contact with the light transmitting cover and is located between {TAIL ~ the first envelope} and the cover 
is located between
{ HEAD ~ The spacer } means is in operative contact with the light transmitting cover and is located between { TAIL ~ the first envelope } and the cover
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH