ASTM D1729-96 Color Viewing Standard
This is the standard for visual appraisal of colors and color differences of diffusely illuminated opaque materials.
Objective of the Standard
The color and appearance of materials is dependent on the geometry, quantity and spectral nature of the illumination as well as the surround conditions/viewing environment. The ASTM D1729-96 viewing standard specifies the conditions for the critical visual color appraisal for color matching. The use of spectrally dissimilar illumination sources allows effective detection of a “conditional” or metameric color match (a good color match under one light source but a color mismatch under a different light source). An equally important function of the standard is to allow effective communication of color between parties working together on color critical projects.
Considerations of the Standard
Quality of Simulated Daylight
CIE D65 - Average North Sky Daylight
The standard specifies this source for color matching applications. Prior to the 1990�s, D75 was specified as the standard source in the USA. In the graphic arts and photography industries, D50 is the standardized source and is referenced in ISO 3664.
Spectral Power Distribution: Daylight
The true "fingerprint" of a light source, spectral power distribution is the key factor in how a light source renders colors. The closer a light source's spectral power distribution is to D50 the more accurate it is. CRI and CIE51 tests are used to insure that your light source closely approximates D65.
Chromaticity
Chromaticity is the apparent color of a light source. Each daylight source has an aimpoint and circular tolerance specified in CIE color space (UCS 1976).
CIE Publication 51 Rating (BC)
This rating specifies how well a light source simulates daylight. The minimum rating is “BC” where the first letter represents the visual portion of the light source and the second letter represents its ultraviolet portion.
Color Temperature (6500K/D65)
Correlated color temperature is the relation between the color emitted by a black body radiator when heated to a specific temperature. It is measured in the Kelvin temperature scale.
Additional Light Sources (Metamerism)
Various light sources are described in the ASTM D1729-96 viewing standard, including artificial daylight (D50, D65 and D75), incandescent (specifically illuminant A and a light source at 2300K), cool white fluorescent (CWF) and other sources as required, which include various types of fluorescent lamps available to the industry. We offer each of the standard sources as well as most of the fluorescent sources. A combination of the sources (specifically D65, CWF or TL84, and illuminant A) is ideal for detection of metamerism.
Light Intensity
Consistent light intensity is critical to consistent color evaluation. This standard provides a target intensity range designed to allow full tonal visibility of dark samples without overilluminating light samples.
Light Evenness
Even light intensity across the sample assures correct interpretation of color quality.
Surround
Surround color and reflectance affect color appearance. In order to assure consistent color appearance and tonal range, the surround condition is specified.
Geometry
The presence of excessive glare can be distracting to observers attempting to make critical color judgments. Glare can influence color perception and result in very costly errors. Likewise, the effects of geometric metamerism, if not taken into account in evaluation observations, will result in color mismatches.