Color Rendering Index - Test Method

Test Method

The CRI is calculated by comparing the color rendering of the test source to that of a "perfect" source which is a black body radiator for sources with correlated color temperatures under 5000 K, and a phase of daylight otherwise (e.g. D65). Chromatic adaptation should be performed so that like quantities are compared. The Test Method (also called Test Sample Method or Test Color Method) needs only colorimetric, rather than spectrophotometric, information.

  1. Using the 2° standard observer, find the chromaticity co-ordinates of the test source in the CIE 1960 color space.
  2. Determine the correlated color temperature (CCT) of the test source by finding the closest point to the Planckian locus on the (u,v) chromaticity diagram.
  3. If the test source has a CCT<5000 K, use a black body for reference, otherwise use CIE standard illuminant D. Both sources should have the same CCT.
  4. Ensure that the chromaticity distance (DC) of the test source to the Planckian locus is under 5.4×10−3 in the CIE 1960 UCS. This ensures the meaningfulness of the result, as the CRI is only defined for light sources that are approximately white.
  5. Illuminate the first eight standard samples, from the fifteen listed below, alternately using both sources.
  6. Using the 2° standard observer, find the co-ordinates of the light reflected by each sample in the CIE 1964 color space.
  7. Chromatically adapt each sample by a von Kries transform.
  8. For each sample, calculate the Euclidean distance between the pair of co-ordinates.
  9. Calculate the special (i.e., particular) CRI using the formula
  10. Find the general CRI (Ra) by calculating the arithmetic mean of the special CRIs.

Note that the last three steps are equivalent to finding the mean color difference, and using that to calculate :

Read more about this topic:  Color Rendering Index

Famous quotes containing the words test and/or method:

    “I have come to believe ... that the stage may do more than teach, that much of our current moral instruction will not endure the test of being cast into a lifelike mold, and when presented in dramatic form will reveal itself as platitudinous and effete. That which may have sounded like righteous teaching when it was remote and wordy will be challenged afresh when it is obliged to simulate life itself.”
    —Jane Addams (1860–1935)

    “Unlike Descartes, we own and use our beliefs of the moment, even in the midst of philosophizing, until by what is vaguely called scientific method we change them here and there for the better. Within our own total evolving doctrine, we can judge truth as earnestly and absolutely as can be, subject to correction, but that goes without saying.”
    —Willard Van Orman Quine (b. 1908)