Why Do Lights Look Different Even at the Same 3000K? — An Interpretation of the Guangzhui COB Color Consistency Standard

This article will use accessible language to clearly explain how to compare colors, industry color tolerance standards, the differences between ANSI and IEC, as well as light cone color standards and the methods used for sample-based inspection.

I. Color Temperature Can Describe "Hue," But Cannot Directly Measure "Color Difference"

Let's first look at a common misconception: even if the color temperature measurements of three different light sources all fall exactly at 3000K, they may still exhibit noticeable differences—appearing distinctly yellowish, reddish, or greenish. This is because Color Correlated Temperature (CCT) is, in essence, a "simplified metric" for a light source's spectrum or hue; while it can describe the general direction of the color, it struggles to fully and accurately reflect the color's precise position on a chromaticity diagram.

II. How Do We "Quantitatively" Compare Color Differences? — Using Color Tolerance (MacAdam Ellipse)

To transform the subjective perception of "looking slightly different" into a "quantifiable difference," the industry typically employs the MacAdam ellipse to define "color difference steps."

• The smaller the ellipse "step" value: the better the color consistency.
• The larger the step value: the more pronounced the color difference.
• Common international requirements generally stipulate that color tolerance must be kept within 5 steps (specific requirements depend on the applicable standards or client agreements).

III. Industry Requirements for Color Tolerance: How Do ANSI, IEC, and National Standards Define Them?

Under different regulatory frameworks, common requirements typically include:

• ANSI: Typically controlled within a 7-step MacAdam ellipse.
• Relevant EU Directives: Commonly follow the 6-step national standard.
• GB/T: For example, requirements may specify a 7-step tolerance or impose further constraints on coordinate differences (such as specific thresholds for u’v’ differences).
• GB/T 29295-2012: Commonly requires a tolerance of 5 steps or fewer.

Among these, ANSI represents American standards, while IEC represents standards from the International Electrotechnical Commission. Notably, the central coordinate points (reference points) for fluorescent lamps and LEDs differ under ANSI standards, whereas they are consistent under IEC standards. GB represents Chinese national standards; currently, most mainstream international LED manufacturers use the ANSI C78.377 standard as their primary benchmark.

You can interpret this as follows: regardless of the standard system used, the "degree of uniformity desired by the customer" ultimately boils down to—and is defined by—the "number of steps" or the "elliptical tolerance range."

IV. Why do different standards "calculate different color tolerances" for the same correlated color temperature (CCT)? — The Difference in Center Points Between ANSI and IEC

This is a common pitfall that many customers and equipment operators tend to encounter:

ANSI and IEC utilize different central points (chromaticity coordinate references); consequently, the exact same set of measurement data will yield different "step deviation" results when evaluated against these different standards.

An Illustrative Example:

• Using the ANSI center point, a specific point might fall within an elliptical range corresponding to a "smaller step number."
• If switched to the IEC center point, the *same product*—when subjected to calculation—might appear to fall into a range corresponding to a *larger* step number.

Therefore:

If your inspection equipment or software does not utilize the specific set of standard center points mandated by your client or the relevant protocol, the resulting judgment may deviate from the true consistency requirements.

V. How Does Guangzhui Standardize the Delivery of "Light-Color Consistency"? — The Evolution from 3-Step to 2-Step Tolerance

What clients ultimately require is this:

That the purchased COBs (Chip-on-Board) or LED beads exhibit the greatest possible consistency—both to the naked eye and at the application level—across different production batches.

Guangzhui’s core philosophy emphasizes the following:

Through rigorous process control and consistency management, we continuously advance our color tolerance capabilities toward stricter tiers (e.g., progressing from higher-step requirements to lower-step requirements), while simultaneously mitigating the cost pressures typically associated with meeting such stringent standards.

The core logic can be summarized in three key points:

1. **Finer Consistency Targets:** Moving beyond mere "usability" toward a state of "stable and uniform consistency."
2. **Matching Process Capabilities:** Ensuring that manufacturing processes and capabilities keep pace; otherwise, aiming for lower-step tolerances will inevitably lead to issues regarding yield rates and production costs.
3. **Customizable Yet Controllable:** Possessing the ability to customize color specifications according to client requirements while simultaneously maintaining absolute consistency across different production batches.

VI. Guangzhui’s Light-Color Standards: What Do ANSI/A, IEC/I, Guangzhui Standard/R, and Guangzhui Bright Color/B Represent?

When you discuss "light-color consistency," the ultimate focal points are:

The Center Point (CIE-X / CIE-Y), the Duv value (deviation), and their corresponding elliptical ranges or "Binning" categories.

Within the Guangzhui system, common standard types include:

• ANSI/A: Corresponds to the center point and Duv definitions of the ANSI system
• IEC/I: Corresponds to the center point and Duv definitions of the IEC system

• Guangzhui Standard/R: The center point/deviation direction established by Guangzhui specifically for consistency control purposes
• Guangzhui Vivid/B: A standard definition tailored for "vividness" (or a visual color presentation with a specific chromatic bias)

VII. Spectral Binning Zones: Why does "Binning" ensure better batch-to-batch consistency than simple Correlated Color Temperature (CCT)?

You can conceptualize a "Bin" as:

A "deliverable consistency zone" delineated by elliptical boundaries on a chromaticity diagram.

The Binning strategy emphasized by Guangzhui includes the following elements:

• Based on the principles of ANSI color region classification, the overall step range is further subdivided into multiple individual "Bins."
• Depending on the specific consistency requirements of different customers, we select either "Single-Bin Shipment" or "Combined-Bin Shipment."
• When combining Bins, the requirement is to perform "Adjacent Bin Combination," while also strictly controlling the maximum allowable number of combined Bins.
• Bins exhibiting color shifts—such as MKO, LJM, etc.—may be utilized for customers whose consistency requirements are not extremely stringent.
• Any products failing the chromaticity coordinate specifications are strictly prohibited from proceeding further in the workflow and are immediately designated for scrap processing.

VIII. How Can Customer Inspection Be Made More Reliable? — Utilizing Guangzhui Standard COB Samples for Golden Samples and Center Point Constraints

The final "practical implementation method" is absolutely critical:

Due to inherent discrepancies in standards and equipment, the "color tolerance steps" calculated for the exact same product may not be entirely consistent when measured on different testing devices.

Licone’s Recommended Procedure:

1. Licone provides a standard COB light source to the client for sample verification.

Once approved by the client, this establishes the "reference center point."

2. During subsequent incoming inspections by the client:

First, perform a measurement using the standard COB source and record the color tolerance value as A.

Next, perform a spot check on the actual shipment and measure the color tolerance value, recording it as B.

3. The shipment is deemed acceptable provided that: (A − B) / 2 < n + 1

Where 'n' represents the number of color tolerance steps (MacAdam steps) specified by the client.

This formula is designed to account for equipment measurement uncertainty.

Special Note: The center point of the color tolerance measurement equipment must remain constant (otherwise, the comparison will be "skewed").

Much like the ruler shown in the image above—even though a section is broken off—we can still determine that the length of the arrow is L = 5 cm, because L = 12 cm − 7 cm = 5 cm.

IX. Why Does "Color Temperature Drift" Occur? How Does Licone Address This Issue from a Process Perspective (Before and After Encapsulation, Dispensing, and Curing)?

In addition to consistency between production batches, variations *within* a single batch or during the manufacturing process itself can also impact the final color output:

LED packages are prone to exhibiting "color temperature drift" during the stages immediately before and after the encapsulation, dispensing, and curing processes. This phenomenon is particularly pronounced in larger-sized LED packages (such as the 5050, 5730, and similar types).

The primary causes typically stem from the following factors:

• Uneven heating during the curing process of the encapsulating resin, leading to variations in curing rates.
• Settling or uneven dispersion of phosphors within the resin.
• Consequently, inconsistent light refraction patterns emerge, resulting in chromatic dispersion and color drift.

Potential solutions include:

• 1. Controlling the acceptable color temperature range: Typically, the color temperature is set to fall within ±10% of the target value.
• 2. Employing a multi-stage baking process: For instance, a three-stage process—Stage 1: 60°C for 1 hour; Stage 2: 110°C for 0.5 hours; Stage 3: 150°C for 3.0 hours—allows for a gentler resin curing transition and ensures more uniform overall curing.
• 3. If a two-stage curing process is utilized, anti-settling agents can be added to the resin mixture to mitigate color drift caused by uneven phosphor sedimentation.

Conclusion

Both samples are rated at "3000K," yet why do their colors differ?

The answer lies in this: Color temperature serves merely as a starting point; the true determinants of color consistency are chromaticity coordinates, color tolerance (MacAdam ellipses), and the corresponding standardized specifications and Binning delivery protocols.

By seamlessly integrating color standards, Binning rules, sample verification procedures, and process controls, Guangzhui aims to ensure that clients achieve superior batch-to-batch color consistency while simultaneously minimizing communication overheads.