Analysis of LED color tolerances from international standards
2017-11-23

Color tolerance definition and MacAdam ellipse explanation

Color tolerance: Characterize the difference between X, Y values and standard light sources calculated by the optical color detection system software. The smaller the value, the closer the light color coordinates and the standard value of the product are. The smaller the difference between the spectrum emitted by the light source and the standard spectrum, the higher the accuracy and the more pure the light color.

MacAdam ellipse explanation: In 1942 scientist MacAdam experimented with 25 colors using the correlation principle, measuring about 5 to 9 contralateral directions per color point, recording the distance between two points when they were just able to tell the color difference, The result is some of the size of different sizes, ranging from the long axis of the ellipse, called the Macadamy ellipse. The MacAdam ellipse is usually described by "order," and the "order" referred to here is actually the standard deviation. The 1-step MacAdam ellipse refers to the standard deviation of the change in the color matching result that is 1 time from the target color. By the same token, the meanings of the 3rd order, the 4th order, and the like are known.

Color tolerance main standard categories

At present, the main color tolerance standards in the United States are North American ANSI standards, IEC, EU standards, the corresponding color tolerance center points are summarized as follows:

The corresponding color tolerance of the corresponding color temperature range

Industry standard level:

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

2. EU standard ERP, color difference ≤ 6 SDCM, in accordance with the technical requirements to regulate LED LED area.

3. National standard GB10682-2002, double-ended fluorescent lamp performance requirements Color Difference ≤ 5 SDCM, LED lamp color tolerance requirements as a reference.

About color tolerance problem test note:

1. It can be seen from the figure that there are differences between IEC and ANSI standard center points, of which 6500K, 3000K and 2700K are obviously different. Therefore, it is necessary to confirm what standard to use for the order (currently, the same party is tested according to the IEC standard and can also choose other standard).

2. Select the corresponding color temperature color tolerance center coordinates, such as 6500K color temperature 2700K standard test color tolerance will be large (some machines will automatically select).

The difference between color tolerance and color difference

Color difference: the color difference, that is, two light color X, Y coordinate value of the size of the difference, the smaller the difference, the smaller the color.

Color tolerance: Characterization of product X, Y value and the standard light source X, Y value difference between the smaller the distance, the smaller the color tolerance.

Description: A (sample) is 3 steps, B is 3 steps, and D is 5 steps. A-B chromatic aberration (X = +0.0099, Y = +0.0148) , Y = -0.0041), but the A-B color tolerance is equal, A-D color tolerance difference of two, so the color tolerance and color difference can not be confused concept.

Color tolerance and color of the intersection of contact

MacAdam proved through experiments that it was only a linear relationship between the standard deviation corresponding to the color matching and the perceived color difference, which was 3 times of the standard deviation. If the two color coordinates fall within 2 MacAdam ellipses, the human eye can hardly see the difference between the two. The difference between the color corresponding to the 3-step MacAdam ellipse border and the center color is exactly perceptible color difference value of the human eye. If the color center of the product happens to be the color tolerance center point, the color tolerance can be used to characterize the color difference and color The larger the tolerance, the greater the color difference.

Description: The correspondence between color temperature and color tolerance causes some problems

example 1. If customers need 3000-3300K products, the European standard and the color tolerance is less than 5 (2820-3070K), then meet the requirements of the range of only about 70K color temperature, the product is difficult to meet the demand.

Example 2. If customers need 5700-6300K products, the European standard and the color tolerance is less than 5, then meet the requirements of the range of only about 200K color temperature, the product is difficult to meet the demand.

Machine tolerance caused by the color tolerance shift problem

If there is a big deviation between the two standard parts of the machine, even if the color difference with the same standard, but the test values vary greatly, not the center of the color tolerance coordinates are not the same value, but the machine deviation caused by the center point Move, it is recommended to confirm the standard.

About the whole color tolerance ≤ 3 SDCM product realization scheme

1. To enhance the order color focus, with the tolerance of the center of the color point of the product as the center of color, lamp beads as much as possible concentrated in the third color range;

2. For SMD and IML orders, the color difference of some products may fall into the range of 3-5 steps, and can be classified according to the color difference and differential optical methods, and cross the SMT to achieve the requirement of the entire color tolerance is less than 3, The same party photoelectric technicians can provide you with the best with the program.

Article from China Semiconductor Lighting Network

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