the diffuser elements have {HEAD ~ an average space therebetween} of {TAIL ~ 50 μm} to 300 μm, 
of
the diffuser elements have { HEAD ~ an average space therebetween } of { TAIL ~ 50 μm } to 300 μm ,
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH