{HEAD ~ Each grey level signal} causes {TAIL ~ a particular proportion} of pixels to be illuminated, in order to produce a particular grey level 
{ HEAD ~ Each grey level signal } causes { TAIL ~ a particular proportion } of pixels to be illuminated , in order to produce a particular grey level
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH