5 Minutes to Let You Know SDCM!
What is SDCM?
“Standard Deviation of Colour Matching” (SDCM) is an important metric used to measure the color consistency of LED light sources. It indicates how much the actual color (measured x, y coordinates) deviates from the standard color point — usually represented as an ellipse on the chromaticity diagram.
In short, the smaller the SDCM value, the more uniform and accurate the light color appears.
A low SDCM means the LED’s color is very close to the target standard, with minimal variation between different lamps, resulting in a more natural and consistent light.
What Does SDCM Stand for?
Within the MacAdam ellipse, even subtle shifts in color go undetected by our eyes. Nevertheless, the human eye can easily distinguish these differences once the color coordinates fall outside this ellipse. Consequently, we can assume that the color of each point is essentially the same as long as it remains within the MacAdam ellipse.
MacAdam Ellipses Definition
MacAdam ellipses are often described using “steps,” where “steps” refers to standard deviation. A 1 step MacAdam ellipse represents the standard deviation of a color match result that is 1 times the standard deviation of the target color (as shown in Figure 1). Similarly, the meanings of 3 step, 4 step, and so on can be understood. If two color coordinates fall within a 1 step MacAdam ellipse, the human eye can barely discern any difference between them. The difference between the colors at the edge of a 3 step MacAdam ellipse and the center is the color difference that is just perceptible to the human eye.
1 step MacAdam ellipses are very small. In most cases, we see scaled-up versions of these ellipses, typically 7 or 10 times the size of the 1 step ellipse. Figure 2 shows a 7x magnified MacAdam ellipse. Each circle in the figure represents a standard deviation of 7 times the standard deviation of the color match result relative to its center color point. This means that the standard deviation between the two corresponding color points at the ends of the ellipse is actually 14 times the standard deviation of the original ellipse.
What is SDCM in Lighting
The following figure illustrates SDCM in LED lighting using 7-step, 5-step, 3-step, and 2-step MacAdam ellipses at a color temperature of 3000K. Within the 3-step MacAdam ellipse, the color difference is almost invisible to the human eye, while the 5-step and 7-step ellipses show more noticeable variations. The 3-step MacAdam ellipse is generally considered the critical threshold for human color perception.
The Applications of Step:
Step 1: Minimal color deviation (1 standard deviation), suitable for high-precision applications (such as high-end displays and medical equipment).
Step 3: General industrial standard (such as LED lighting and printed materials).
Step 5: Low-demand applications (such as general consumer products).
Standard of SDCM
At present, the main color tolerance standards in the lighting industry are set by North America’s ANSI standards and Europe’s IEC standards. These standards define how much variation in color is acceptable for SDCM LED light sources to ensure consistent visual performance.
North American ANSI C78.376 Standard
According to the ANSI C78.376 standard, the color consistency of LED products must fall within SDCM ≤ 7. In this system, the chromaticity diagram is divided into different regions that represent various color temperatures and light characteristics. This allows manufacturers and users to easily identify whether an LED’s color is within the acceptable range for a specific application — ensuring that lights from different batches appear uniform to the human eye.
European IEC 60081 Standard
Under the EU IEC 60081 and ERP (Energy-related Products) standards, the color tolerance requirement is even stricter, typically SDCM ≤ 6. This means the European market demands higher precision in color control. LEDs are classified and tested according to specific lighting technology requirements to ensure both visual comfort and consistency across different lighting fixtures.
In general, the lower the SDCM value, the more consistent the light color will appear, even when multiple fixtures are installed side by side.
The corresponding color temperature ranges for different SDCM levels help engineers and lighting designers choose LEDs that best meet their needs — balancing color accuracy, energy efficiency, and cost.
The color temperature ranges corresponding to the SDCM are as follows:
TThe color temperature ranges of the ANSI and IEC standards are different. Shinelong Technology will use LEDs of corresponding standards according to the different markets of customers.
Shinelong has strict requirements for SDCM in lighting and adheres to rigorous procurement standards, purchasing only LEDs from 2 Bin or fewer. In particular, we use only 1 Bin LEDs for panel lights. Through meticulous LED binning and color consistency control, we ensure excellent product performance and achieve highly consistent correlated color temperature.
For LED light, we can directly obtain their color coordinates X/Y values through integrated sphere testing. Based on these measurements and using various calculation tools, we can determine the distance between the LED lamp and the standard color temperature coordinate point, and then determine the ellipse step to which it belongs, namely the SDCM.
Factors Affecting SDCM in LED Lighting
A smaller SDCM value means tighter color consistency and more uniform lighting performance.
Structure
Taking panel lights as an example, optimizing the structure of the light guide plate, reflective paper, and diffuser can improve light uniformity and thus reduce SDCM.
LED Luminaire Heat Dissipation
If the light heat dissipation is insufficient, rising temperatures can cause color shift. LED light materials exhibit significant temperature dependence. As the emission temperature rises, the emission spectrum red shifts, the emission peak broadens, and even quenching occurs. Therefore, improving heat dissipation is crucial for reducing color tolerance.
LED Forward Current
The properties of LED luminescent materials are affected by changes in driving current. LEDs with higher luminous stability have less influence on color temperature due to current, resulting in lower color tolerance.
At ShineLong, we maintain exceptionally strict standards when selecting LED chips and controlling production quality. For example, in our LED panel lights, we use only one bin of LED chips. This ensures that no matter when or in how many batches customers purchase our products, the lighting will always maintain consistent color within the same color temperature range.
What is The Difference Between CRl and SDCM?
CRI and SDCM describe two different aspects of light quality. CRI (Color Rendering Index) measures how accurately a light source reveals the true colors of objects compared to natural light—the higher the CRI, the more natural the colors appear. SDCM (Standard Deviation of Color Matching), on the other hand, measures color consistency between light sources; a lower SDCM value means less visible color variation.
In short, CRI relates to color accuracy, while SDCM relates to color uniformity.
Methods for Reducing SDCM
If two testing machines have different standard parts, even when they use the same color tolerance (SDCM), their test results can be very different. This may cause color differences between LED batches. To avoid this problem, it’s best to do a benchmarking check between the machines. This helps make sure both machines give similar and reliable results, keeping the color quality stable.
To make LED colors more consistent, use the center point of each color range as the target color. Try to keep all LEDs within a 3-step SDCM range. This helps reduce color differences between products and makes the light look more even and natural.
Color variation in LED lights is unavoidable, but customers should select high-quality LEDs and minimize color variation during the production process to improve the uniformity of light emission and the concentration of LEDs. Furthermore, reducing color variation requires scientific and rational methods, close collaboration between LED chip manufacturers and lamp manufacturers, the introduction of demanding industry standards, and the updating of technical specifications by testing agencies and equipment.
At ShineLong, we place great emphasis on color consistency. By strictly controlling LED binning and sourcing from reputable suppliers, we ensure uniform light output across every product.
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