ASTM International

Standard Practice for Goniometric Optical Scatter Measurements
 N E2387

Annotation

This practice describes procedures for determining the amount and angular distribution of optical scatter from a surface. In particular it focuses on measurement of the bidirectional scattering distribution function (BSDF). BSDF is a convenient and well accepted means of expressing optical scatter levels for many purposes. It is often referred to as the bidirectional reflectance distribution function (BRDF) when considering reflective scatter or the bidirectional transmittance distribution function (BTDF) when considering transmissive scatter.

The BSDF is a fundamental description of the appearance of a sample, and many other appearance attributes (such as gloss, haze, and color) can be represented in terms of integrals of the BSDF over specific geometric and spectral conditions.

This practice also presents alternative ways of presenting angle-resolved optical scatter results, including directional reflectance factor, directional transmittance factor, and differential scattering function.

This practice applies to BSDF measurements on opaque, translucent, or transparent samples.

The wavelengths for which this practice applies include the ultraviolet, visible, and infrared regions. Difficulty in obtaining appropriate sources, detectors, and low scatter optics complicates its practical application at wavelengths less than about 0.2 m (200 nm). Diffraction effects start to become important for wavelengths greater than 15 m (15 000 nm), which complicate its practical application at longer wavelengths. Measurements pertaining to visual appearance are restricted to the visible wavelength region.

This practice does not apply to materials exhibiting significant fluorescence.