Partitioning the Color Space – Binning
Phosphor-based illumination sources exhibit greater variability than other sources such as tungsten or halogen. Binning systems first
emerged to characterize phosphors and more recently to characterize white LEDs. LED manufacturers adopted binning techniques to
offer consistent characterization of their manufactured output.
Though manufactured to exceedingly tight tolerances at every step from wafer production to component packaging, there are natural
variations in material and processes that dictate the photometric properties of white LEDs. Material characteristics vary over the surface
of a wafer and so into the individual LED die. Binning characterizes the output of manufacturing processes and lets customers develop
strategies to work with this output and achieve uniform illumination sources. Cree’s basic binning nomenclature and definitions follow
the ANSI C78.377-2008 LED binning standard. The location, shape, and size of these bins have a rough conformance to the varying axial
orientation and sizes of MacAdam ellipses.
In response to demands of the lighting industry, LED manufacturers have rapidly improved product uniformity and distribution. Cree
developed the XLamp LED bins by segmenting the ANSI bins in an effort to reduce color variation.
Figure 11 shows an example of the bin of a 3200-K product and illustrates a practical example of the bins. The center of the bin is (0.4245,
0.3999) around the intersection of the black body line and the 3200-K gradient line. The boundaries of the parallelogram are displayed in
the illustration