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