Integrating sphere geometry spectrophotometers utilize a reflecting sphere to capture the reflected light from a sample. The reflected light leaves the sphere through a viewport and is analyzed by a detector array. The detectors measure the percent reflectance across the visible spectrum, usually at 10 nanometer increments.

Sphere spectrophotometers are the only instrument capable of separating out surface and appearance effects to measure only the color of an object. Additionally, in Specular Component Excluded (SCE) mode, a sphere spectrophotometer can simulate visual assessment through measurement of color and appearance combined.

SABIC uses GretagMacbeth ColorEye® 7000 and 7000A sphere geometry spectrophotometers exclusively in its global color operations based on their excellent repeatability and inter-instrument agreement.

Advantages

• Can measure transparent and translucent samples.
• Can measure fluorescent samples.
• Can measure color and appearance separately.

Disadvantages

• Data may not agree exactly with 0/45°, etc.
• Specular removal not 100 percent.

It is important to note that even with the latest technology and with good instrument maintenance, readings from different spectrophotometers will not agree perfectly. Quarterly independent lab testing (which SABIC participates in) consistently indicates that out of an industry population of over 250 integrating sphere spectrophotometers, measurement standard deviations are 0.1 to 0.25 CIELab units for absolute color measurements and up to 0.15 CIELab units for color difference measurements.

The Reflectance Curve

The spectrophotometer reflectance curve of a sample is the identifying fingerprint of that sample! The location of inflection points and the slopes of the curve describe the color. To the experienced colorist, the curve is also an indication of the colorant mixture components. Therefore, the spectrophotometer curve can be an indispensable tool to the colorist.

[< Prev]    [Next >]