a substantially constant light path providing layer consisting essentially of a diffusely reflecting material that i) is sufficiently porous in all directions as to allow a liquid to spread uniformly in all directions, and ii) homogeneously and diffusively reflects {HEAD ~ at least 95%} of {TAIL ~ NIR radiation}, 
a substantially constant light path providing layer consisting essentially of a diffusely reflecting material that i ) is sufficiently porous in all directions as to allow a liquid to spread uniformly in all directions , and ii ) homogeneously and diffusively reflects { HEAD ~ at least 95 % } of { TAIL ~ NIR radiation } ,
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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH