For {TAIL ~ a highly precise measurement} of even low light intensities for {HEAD ~ the purpose} of reduction of the analysis time, each light source is switched on and off during a defined interval by a clocked pulse sequence of constant pulse frequency alternately 
For { TAIL ~ a highly precise measurement } of even low light intensities for { HEAD ~ the purpose } of reduction of the analysis time , each light source is switched on and off during a defined interval by a clocked pulse sequence of constant pulse frequency alternately
OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH