Conclusion – what influences the different dot distribution?
LED Module Binning / SDCM
Natural colour tolerances between LEDs (even within the same
M930) cause subtle differences in chromaticity. Nonetheless all three
samples would fit into 2nd MacAdam elipse – not possible to detect
with the naked eye, even in case of a trained observer (e.g. laboratory
technician, lighting designer)
Optics and Reflector
Different reflectors modify the spectrum and angular distributions,
resulting in subtle chromaticity shifts (angular colour shift). Even
with the same source, different optical geometry = different colour
distribution in the field.
Moreover, chromaticity is not the only parameter affecting light
perception. Luminance is a major factor in how humans perceive
a lighting effect. For example, three luminaires with different beam
angles could all be within an SDCM tolerance of 2, yet their distinct
light patterns create different final effects on an illuminated wall. Rings
(Black vs. White Finish)
The black finish reduces stray light and internal reflections, reducing
the impact of indirect light on the result—the dots on the SDCM
diagram tend to cluster more tightly than in variants with a white ring.
Thermal Conditions and Supply Current
LED junction temperature and minor differences in current can slightly
shift the chromaticity (Δx, Δy) during measurement.
Production Repeatability of Optical Elements
Differences in reflector layers (e.g., coating thickness/type, shape
tolerances) also introduce small but measurable shifts.
Summary:
The three points within the 3-step (SDCM 3) show typical, catalogue-
acceptable colour variation for this configuration: the light is visually
consistent enough in most applications, with variations primarily due
to a combination of LED tolerances (binning) and the effects of the
optics/measuring environment.
Very tight requirements for SDCM are costly, but might be very
important in very large or long rooms (e.g. corridors) where dozens
of single luminaires or very long, continuous luminous surfaces are
visible at once against a uniform background, especially when finished
in white. Low SDCM is also very important in specialistic application
like art, photography, colour matching or assessment.
In overwhelming majority of day to day cases SDCM 3 is sufficient
both in terms of aesthetics and correct performance of visual tasks.
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