About SDCM

Color Tolerance: Characterizes the difference between the X and Y values calculated by the software of the photochromatic electric detection system and the standard light source. The smaller the value, the closer the product light color coordinates and the standard value, the smaller the difference between the spectrum emitted by the light source and the standard spectrum, the higher the accuracy, the purer the light color.

McAdam ellipse theory: 1942 scientists McAdam use the principle of correlation on 25 kinds of color experiments, in each color point about 5 to 9 opposite side of the direction of the measurement, record them just to be able to distinguish the difference between the color of the distance between the two points, the result is that some of the area of the size of the various, the length of the axis of the ellipse is not the same, known as the McAdam ellipse. McAdam's ellipse is usually described by ‘step’, where the ‘step’ refers to the standard deviation. 1 step McAdam's ellipse refers to the distance from the target color 1 times the standard deviation of the change in the results of the color matching, and similarly can be seen, the meaning of the 3 step, the 4 step.

The main standard categories of color tolerance

 At present, the main standards for color tolerance are the North American ANSI standard, IEC, EU standard.

Industry standard level

1. Energy Star ANSI C78.376, color tolerance ≤ 7 SDCM, according to the LED characteristics of the region.

2. EU standard ERP, color tolerance ≤ 6 SDCM, according to the technical requirements to regulate the LED division area.

3. China National standard GB10682-2002, double-ended fluorescent lamp performance requirements for color tolerance ≤ 5 SDCM, can be used as a reference for LED lamp color tolerance requirements.

Comparison of IEC standard and ANSI standard 3step schematics

Note on color tolerance test

1. As can be seen from the figure: IEC and ANSI two standards have differences in the centre point, of which 6500K, 3000K, 2700K difference is obvious, so the order must first confirm what standard to use (at present, the same side of the photoelectric in accordance with the IEC standard test, but also according to the customer's needs to choose other standards). 

2. Select the corresponding color temperature band color tolerance centre point coordinates, for example, 6500K color temperature selection 2700K standard test color tolerance will be very large (some machines will be automatically selected).

The intersection between the color difference and SDCM

McAdam experimentally proved that the difference between the perceptible color difference and the corresponding standard deviation of the color match is linear, and three times the standard deviation is the perceptible difference of the color difference. If the two-color coordinates fall within the 2nd order McAdam's ellipse, the human eye can hardly see the difference between the two is what the difference. 3 order McAdam's ellipse boundary corresponding to the color and the center of the color difference is the human eye just perceptible color difference value, if the product color center point happens to be the center of the color tolerance, then you can use the color tolerance to characterize the color difference, the larger the tolerance, the greater the difference in color.