Both test methods measure specular gloss and haze together at 20° that means light is transmitted and received at an equal but opposite angle of 20°.
Specular gloss is measured over an angular range that is limited by aperture dimensions as defined in ASTM Test Method D523.
As test method ASTM D4039 is only suitable for nonmetallic materials of more or less the same refractive index separation of the colour and haze components is not detailed.
Both ISO 13803 and ASTM E430 method B require a separate measurement of luminous reflectance, Y, to calculate compensated haze.
The tri-stimulus value Y gives a measure of the lightness of the material as defined in ISO 7724-2 requiring a 45°/0° geometry to be used with standard illuminant C and 2° observer (although it is mentioned that slightly different conditions will not result in significant errors).
Using a measurement angle which is closer to the region adjacent to the haze angle has proven successful in providing compatible readings on solid colours and also compensating for directional reflection from metallic coatings and speciality pigments Generally measurement of reflection haze is confined to high gloss paints and coatings and highly polished metals.
This causes the light to scatter in different directions from the normal the degree of which being related to the size and number of irregularities present.
These factors are therefore important for defining the transmitting properties of a transparent material- Transmission – The amount of light that passes through the material without being scattered Haze – The amount of light that is subject to Wide Angle Scattering (At an angle greater than 2.5° from normal (ASTM D1003)) Clarity – The amount of light that is subject to Narrow Area Scattering (At an angle less than 2.5° from normal) Measurement of these factors is defined in two International test standards- ASTM D1003 comprises two test methods:[4] Procedure A – using a Hazemeter Procedure B – using a Spectrophotometer Source:[5] Part 1 – Using a single beam Hazemeter Part 2 – Using a dual beam Hazemeter The test methods specify the use of a Hazemeter as shown below -
The light, which is uniformly distributed by a matte white highly reflective coating on the sphere walls, is measured by a photodetector positioned at 90° from the entrance port.