Top reasons why color instruments don't agree

The increased use of instruments like spectrophotometers in the print industry has created an apparent increase in the level of precision in the measurement and description of color. However, the objective accuracy may not be as it seems - when comparing the measurement results from different instruments - even when coming from the same vendor.

Even when properly calibrated instruments can deliver different measurement values (>DeltaE 7 according to a PIA/GATF study) simply because of how the various instruments respond to the gloss on coated paper, aqueous coatings, UV coatings, and lamination. The use of UV cut filters (as is popular in Europe) can also increase the disagreement between instruments.

The top reasons why color instruments don't agree

• Variations in ambient conditions including instrument Induced sample heating resulting in "thermochromism" where Ink changes color due to a change in temperature and "hygrochromism" because humidity changes the way ink interacts with paper and hence its color.It's a good idea to record temperature and humidity levels whenever measurements are taken.

• Noise introduced by reflectometer instability, instrument and environment induced noise and dark current drift.

• Fluorescence in the substrate coupled with variation in the spectral power distribution of the instrument's illumination - too little or too much UV light.

• Instrument Geometry. There are typically no geometric tolerances on low end instruments. Fiber optic instruments tend to have wide geometric tolerances.

• Spectral bandwidth function may be too narrow or too broad and be too variable from wavelength to wavelength.
• No, or inadequate, black level adjustment. Non-black light trap or directionally sensitive light trap.

• Poor instrument maintenance.

• Infrequent or lack of recertification by factory. Lack of periodic verification