Technical Design-in Guide SLE G6 | 12-2018 | 2.1 | en
Optical Aspects
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An even more accurate approach is to specify the standard deviation from the target colour, based on levels of MacAdam ellipses. The
unit for this is called "SDCM" (abbreviation for "Standard Deviation of colour Matching"). When looking directly into a light source,
these differences are perceived more strongly than in a "normal" situation where light is mainly perceived because of its reflections
from illuminated surfaces.
Colour differences within one level of the MacAdam ellipses are not visible even when looking directly into the light source. Deviations
of two to three levels (<= 3 SDCM) are considered barely perceptible. A value of 3 SDCM is good for LED light sources. For most
applications a value of 5 SDCM is still sufficient .
5.4. Binning
Chips and packages from the same production can still show small variations in colour temperature and forward voltage . If the chips
are used without pre-selection, these differences can be noticable and interfere with the appearance.
Binning means that the chips and packages are classified according to their colour temperature and forward voltage. This leads to
groups of chips or packages that fall into a very narrow window of tolerance. If LED modules are equipped with such chips and
packages differences in appearance can be prevented.
5.5. Secondary Optics
The term Secondary Optics refers to additional optical elements that shape the light output in different forms. Secondary Optics
include e.g. reflectors, lenses or covers.
5.6. Coordinates and tolerances (to CIE 1931)
As before, the production process for LEDs does without binning. As a result, white LEDs can be produced with normal distribution in
the range of a MacAdam-Ellipse 3. Thanks to the proximity to the Planckian curve there are no annoying colour discrepancies.
Every module is automatically tested at the final inspection stage to ensure that all the supplied products fall within the agreed
specification.
