Were LED Color Rendering Standards 10 Years Ago More Advanced Than They Are Today?

In the lighting industry, the metric most frequently cited is CRI (Color Rendering Index). However, if you work in fields such as commercial displays, general retail, art and exhibition spaces, or professional design lighting, you may find that CRI sometimes fails to fully capture whether "colors actually look good under the light."

To address these issues, the IES introduced TM-30-15—a color rendering evaluation method considered more capable of characterizing subtle differences in color appearance. It is gradually being integrated into the workflows of professional lighting designers, and is beginning to replace (or at least supplement) the traditional CRI.

This article will explain—in an easy-to-understand manner—the core metrics of TM-30-15, how it differs from CRI, and how to properly interpret its data.

I. First, Let's Discuss CRI: It Excels at "Broad Comparisons" but Has Significant Shortcomings

CRI (centered on the CIE Ra value) can be understood as a light source's ability to "faithfully render" the colors of objects relative to an ideal or natural light source. Generally speaking, the higher the CRI, the closer the color appearance of common objects under that light source will resemble their appearance under the reference light source.

However, in practical applications, CRI still faces considerable criticism—particularly when the light source has a low color temperature. The reasons for this include the fact that CRI is based primarily on a limited set of color samples and a specific comparison methodology, making it difficult to encompass the richer variety of color variations encountered in real-world scenarios.

Consequently, TM-30-15 was proposed. Its aim is to describe "how colors have changed" from a more comprehensive perspective, rather than simply providing a single numerical score.

II. The Three Core Components of TM-30-15: Rf, Rg, and the Graphic Plot

TM-30-15 is not merely a single "index"; rather, it consists of three main components designed to characterize differences in color rendering with greater precision.

1) Rf: Overall Fidelity (Similar in function to CRI)

· Rf is used to characterize the overall degree of similarity between a set of test colors and a reference light source.

· Range: 0 to 100 (The higher the value, the closer the overall match is to the reference light source).

2) Rg: Average Saturation Shift (Addresses whether colors appear "more vivid" or "more muted/gray")

· Rg measures the average saturation level of the test source relative to the reference source by evaluating the area enclosed by the chromaticity coordinates within multiple hue bins.

· **Neutral (100)** indicates that the saturation aligns with the reference;

o Greater than 100: More saturated, more vivid

o Less than 100: Less saturated, more muted/gray

3) Color Vector Graphic and Saturation Graphic: Instantly reveal "what changed" and "how it changed"

The graphical component of TM-30-15 typically consists of two types of charts, designed to provide a visual understanding of the direction and magnitude of color shifts:

· Color Vector Graphic: Based on the average rendering within each hue bin, this graphic illustrates the shifts in hue and saturation relative to the reference source.

· Saturation Graphic: A simplified view focused primarily on illustrating changes in saturation levels.

The significance of this section lies in the fact that:

You not only know "how good the overall quality is" (Rf), but you also know "in which direction the colors are drifting" (Rg) and "specifically which hues exhibit the most pronounced changes."

III. CRI vs. TM-30-15: Where Exactly Do the Differences Lie?

Many people regard TM-30-15 as merely an "upgraded version of the Color Rendering Index" (CRI); however, it is better described as a comprehensive redesign—spanning everything from the scoring logic to the evaluation dimensions.

Based on the comparative points highlighted in this article, the differences can be summarized as follows:

· Sample Quantity and Color Coverage

o CRI: Centers around a relatively limited set of test colors.

o TM-30-15: Incorporates a much richer and more extensive dataset for color evaluation.

· More Granular Output

o CRI: Tends to focus on a "single fidelity metric" (e.g., Ra).

o TM-30-15: In addition to an overall score, it provides a Gamut Index (Rg) as well as Color Vector and Saturation Graphics, allowing you to visualize the specific "location" and nature of the color shifts.

· Reference Light Sources and Evaluation Methodology

o CRI's reference conversion method may, in certain color temperature scenarios, struggle to accurately reflect actual visual perception.

o TM-30-15 employs a methodological approach that addresses these issues in a manner more closely aligned with real-world conditions (as the article emphasizes, this standard was specifically introduced to resolve the limitations inherent in CRI).

IV. Why Is TM-30-15 More Worthy of Attention?

The core arguments presented in this article can be summarized in three points:

1. CRI is more prone to "looking impressive on paper, but not necessarily performing well in reality." This is because CRI focuses primarily on the contrast of a limited set of specific reference colors. If a product's light output is "deliberately engineered" to favor these specific colors, its CRI score may be artificially inflated, even though the actual visual experience may not have comprehensively improved.

2. TM-30-15 offers a closer approximation of "how real-world color appearance differs." It provides not only an overall score but also specific details regarding saturation shifts and hue direction, thereby enabling designers to make more informed trade-offs.

3. It is more likely to be adopted in scenarios where "color rendering is a critical metric"—for instance, in applications where specifiers place a premium on visual aesthetics.

In other words: when your objective is to achieve "colors that appear more natural, more stable, and closer to your desired visual outcome," TM-30-15 provides information that is far more actionable.

V. Deciphering TM-30-15: A Quick Guide from Scores to Graphics

If you receive a TM-30-15 report or data sheet from a supplier, you can use the following approach to quickly assess the results:

· First, check the Rf value: Is the overall color fidelity high or low?

· Next, check the Rg value: Do the colors tend to appear more vivid (>100) or more muted/grayish (<100)?

· Finally, examine the graphic visualization: Which specific hues exhibit the most significant shifts? Are there any areas of "color distortion" that are of particular concern to you?

VI. Conclusion: Color Rendering Is Not a Problem That Can Be Solved by a Single Score

While CRI remains prevalent in residential lighting, in professional fields—where the pursuit of precise visual representation is paramount—TM-30-15 is providing a more comprehensive framework for evaluation: overall fidelity (Rf) + saturation shift (Rg) + a color vector graphic.

At Guangzhui Optoelectronics, our goal is to help transform raw "data" into "actionable insights"—ensuring that product selection is not based solely on a single numerical score, but rather aligns more closely with the actual visual experience.

Although there is still a long road ahead for the widespread adoption and implementation of TM-30-15 metrics, Guangzhui is ready to move forward together with you.