# What Is SDCM (Standard Deviation of Color Matching)?

In 1942, scientist McAdam experimented with 25 colors using the relevant principle,
measuring about 5 to 9 opposite sides of each color point, recording the two points when they
were able to distinguish the color difference. The result was some An ellipse of varying sizes
and lengths, called the MacAdam ellipse.

Human-eye-sensitivity-to-color

From the above figure, the sensitivity curve of the human eye to color:
1. The difference in sensitivity of the human eye to the color of the spectrum is non-uniform;
2. According to the recognition of the color of the human eye, the size of the MacAdam ellipse
is also inconsistent in different regions.
McAdam’s ellipse theory: provides a guide to the accuracy of color vision and the goodness
of distinguishing similar colors. The color inside the ellipse represents a range in which the
human eye does not feel that the color changes too much, which is called the full capacity of
the color.

So, in the actual application, how do we quantify the vast capacity of color?
Here, we introduce a concept: SDCM (Standard Deviation of Color Matching).
SDCM: Characterizes the difference between the X and Y values calculated by the optical color
detection system software and the standard light source. The smaller the amount, the closer
the product’s light color coordinate to the standard value, the lower the difference between
the spectrum emitted by the light source and the usual range, the higher the accuracy, the
purer the color of the light.

Known by the definition of SDCM:
a. The color tolerance actually refers to the distance of the measured value from the target
value;
b. An ellipse generally characterizes quantification of color tolerance.
Unit: SDCM (Standard Deviation of Color Matching):

▲ The ellipse in the above illustration can be understood as Step, you can understand it like
this: 3SDCM = 3 Steps. Usually, the human eye can find the difference in 5~7 steps. That is to
say, when SDCM between the light sources is higher than five steps, it will be easily recognized
by human eyes.