Standard Test Methods for Optical Properties

There are a variety international standards related to optical properties of glazing and shading by ISO, CEN and ASTM. There are also national standards in many countries. In the U.S. we often to refer to NFRC technical documents at least until efforts at harmonization are successful.  These standards duplicate each other in many cases and reference each other in a complicated way. Here is an attempt to explain the current state of affairs: