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world leader in LED measurement
Right from the start, we have been supporting the
LED industries with our measurement equipment.
You will also benefit from this expertise in the new
Solid-State Lighting applications. Our solutions
combine highly precise spectroradiometers and
photometers with a complete family of goniometers and integrating spheres.
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CIE 1976 (u', v') diagram
ter-points, an approach similar to the flexible nominal CCTs can
In the current standard, the center-points curve is described
by a mathematical expression of Duv. The mathematical expression consists of the variable Tx — indicating CCT value, two coefficients, and one constant. By varying the constant, the location
of the center-points curve can be moved to below the black-body
locus with negative Duv values, or above the black-body locus with
positive Duv values. The moving distance is measured by the Duv
value. Below the black-body locus it appears to be a pink white,
and above the black-body curve it appears to be a yellow white
for warm white and green white for cool white. The center-points
curve can be moved with a recommended increment and a defined
range. Beyond this range, the color of light is no longer accepted
as white. For any given center-points curve within the range, the
tolerance can be calculated using the existing seven-step or four-step MacAdam ellipse equivalent quadrangles and circles. This
approach may be called flexible Duv, similar to the flexible CCT.
The ANSI committee’s work for continuous improvement of the
chromaticity standard is a great indication of how the standard
and lighting technology and applications are closely related and
how the interested parties collaborate. LED lighting is an evolving technology and user input for preferred or perceived effects,
as well as other human-centric information, is still in the stage to
be gathered, analyzed, and implemented. The standard development community has been actively engaged in this dynamic cycle
from technology to product to standardization, and then further
improvement for the next cycle.
FIG. 3. Results of the NIST experiment plotted on ANSI
C78.377 chromaticity specifications for SSL products. NIST
results were developed according to the most preferred white
points in a typical interior room environment with various
colored objects, when the subjects were fully adapted to the
Source: Y. Ohno and M. Fein for National Institute
of Standards and Technology (NIS T).