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Monday, January 26, 2015

Why do I calibrate to CIE Whiteness AND ISO Brightness on my diffuse spectrophotometer?

The short answer is “Fluorescence!”

Now for the longer answer:

In the mid 1990’s Dr. Tony Bristow was elected to be convenor of ISO Technical Committee 6 Working Group 3.  He took it upon himself to establish calibration for UV levels within ISO 2469 conforming instruments.  At the time there were two distinctly different UV levels in use.  The Technidyne Micro TB-1C and other colorimeters tended to use a UV level that was determined by the QTH (quartz-tungsten-halogen) lamp.  Spectrophotometers with flash lamps tended to use full UV (Datacolor Elrepho 2000’s).  When Dr. Bristow and Technidyne investigated the situation, we found that UV Sources “C” and “D65” tended to come closest to matching the two different UV levels. 

The parameter “Brightness” was used at the UV level “C” because colorimeters had a hard time calibrating to tricolor based Whiteness.  That coupled with the fact that at the UV level C, it did not make much of a difference which parameter you calibrated too (Brightness or Whiteness). 

The parameter “CIE Whiteness” was used at the UV level D65 because it gave the better inter-instrument colorimetric agreement between instruments than did Brightness calibration (tri-colorimetric calibration versus single color calibrations with Brightness).

When you calibrate your ISO 2469 conforming instrument with traceable calibration standards from one of the ISO Authorized Laboratories (Technidyne, FPInnovations, Innventia or CTP), a non-fluorescent 90-range standard is used and a fluorescent standard is used. The fluorescent standard calibrates to UV level C using ISO Brightness and UV level D65 using CIE Whiteness.

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