Home / Standard Deviation Colour Matching, SDCM

Colour difference of 2, 3, 4 SDCM

What is Standard Deviation Colour Matching, SDCM?

SDCM is an acronym which stands for Standard Deviation Colour Matching. SDCM has the same meaning as a “MacAdam ellipse”. 

MacAdam Ellipse

The MacAdam ellipse is a system of colour measurement. It measures how much colour variation is possible around these axes, before the human eye detects a colour change. A series of ellipses can then be drawn around any target colour, and the closer any given lamp is to the target, the less colour deviation will be experienced when these lamps are placed side by side in an installation.

The distance from the target point in each ellipse is measured in SDCM. An SDCM of 1 step means that there is no colour difference between LED chips, 2-3 SDCM means that there is hardly any visible colour difference while 4 or more SDCM is readily noticeable. The lower the number of SDCM, the smaller the color shift.

Classroom and Outdoor Lightings

The requirements for most indoor environments are usually around MacAdam 2-3 SDCM. For most exterior applications, a rating of MacAdam 5 SDCM is perfectly acceptable. 

Cheaper products will often use LED modules that have a range of MacAdam Ellipses beyond four, some going as high as eight. Fixtures using such modules need to be used with care. There may be general commercial of industrial areas where they are acceptable, but any requirement for colour sensitivity would rule them out.

Why is it important?

The color consistency or chromaticity consistency of the light source is important because if you have more than one lamp in close proximity the difference in colour will be noticeable and reflect on the surroundings. Uniformity will not present which could create an undesirable lighting solution.

The problems are greatest when lighting a white surface, or placing a LED strip very close to a white wall.