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Designing with light
Lighting knowledge
LED
Colour consistency (SDCM)

SDCM: colour consistency with LEDs

SDCM MacAdam ellipses

The SDCM (Standard Deviation of Colour Matching) value describes the colour consistency (colour location deviation) of light sources using the MacAdam ellipses as defined by David MacAdam.

Overview of colour consistency (LED)

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What is LED colour consistency?

SDCM: MacAdam ellipses and their importance for wallwashing

Uniform and colour-consistent wallwashing

The colour consistency stipulates how close the actual light colour of an LED is to the defined colour location. When selecting luminaires, lighting designers should ensure that the colour consistency of the luminaires used is as high as possible. This is particularly important when, for example, wallwashing is carried out with several luminaires. On a white wall, even small colour location deviations between the luminaires can be noticed. The unitless SDCM value is used to evaluate colour consistency.

What does SDCM mean?

CIE xy colour space with Planckian locus and SDCM MacAdam ellipses

Depending on the colour location and the extent of colour deviation with different LEDs, our eyes perceive a deviation in colour location either immediately or only very slowly. Deviations at a specific level are no longer perceived.

If areas are drawn around the deviating but unperceived colour location deviations for different LEDs of one colour temperature on a CIE xy chromaticity diagram, ellipses are created. An ellipse describes the limit of perceptibility of colour differences. These ellipses go back to David L. MacAdam, and are thus often called MacAdam ellipses. The size of the ellipses is standardised and their number is communicated via the SDCM value.

Interesting:

The smaller the SDCM value, the lower is the possible deviation of the light colour from the colour coordinates specified in the technical data of the light source.

All LEDs located in the first ellipse are perceived by the viewer as identical with regard to their colour location (SDCM = 1). The LEDs located in the second ellipse and, under certain conditions, also in the third ellipse, are also perceived as the same or very similar. From SDCM = 4, differences are clearly recognised. Since colour location deviations cannot be avoided in LED production, manufacturers of high-quality luminaires make sure that the binning of their LEDs complies to an SDCM value as low as possible.