Question: What is the difference between an ASTM Procedure A and Procedure B Haze meter.
Answer: A very simple explanation is that the design of a Procedure A instrument has a single detector (photopic Y - C/2 or A/2) mounted on the sphere. The light source is opposite the sample sphere opening. This design can only report %Haze or %Total Transmission. It CANNOT report color such as XYZ or CIELAB. This design is the opposite of a HunterLab transmission capable spectrophotometer which has the light source mounted on the sphere and a full range detector and grating opposite the sample sphere opening.
A Procedure B instrument is a transmission capable spectrophotometer, such as the HunterLab VISTA that also must meet a few extra design criteria, such as number and size of openings in the sphere and size of detection beam relative to size of entrance and exit ports of the sphere. The VISTA is fully compliant with ASTM Procedure B.