{HEAD ~ The exposure period} is then set to {TAIL ~ a period} which is a predetermined length of time less than the browning threshold 
is set to
{ HEAD ~ The exposure period } is then set to { TAIL ~ a period } which is a predetermined length of time less than the browning threshold
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH