ANSI/IES TM-30-24 Method for Evaluating Light Source Color Rendition: Three-Dimensional Evaluation Framework and Local Color Performance

The IES TM-30-24 Method for Evaluating Light Source Color Rendition is the latest color quality evaluation standard released by the Illuminating Engineering Society (IES) in 2024, representing a major upgrade to the TM-30-18 standard. In the IES TM-30-24 standard, the color quality evaluation index system has undergone structural upgrades, transitioning from a single dimension to multi-dimensional collaborative evaluation, with particular emphasis on quantifying local color performance and design intent. The IES TM-30-24 standard introduces a new three-dimensional evaluation framework, including Preference (P), Vividness (V), and Fidelity (F) design intent categories, and adds key color rendering index parameters such as local chroma shift (Rcs,h1) and local fidelity (Rf,h1), with Rf and Rg color rendering indices serving as the core evaluation indicators of the IES TM-30-24 standard, providing more precise color quality evaluation tools for lighting design.

I. New Design Intent-Oriented Three-Dimensional Evaluation Framework

IES TM-30-24 is the first to decompose color quality into three design intent categories: Preference (P), Vividness (V), and Fidelity (F), with three priority levels defined for each category (Level 1 being the highest). This framework achieves precise matching of actual lighting needs by combining multiple basic color rendering index indicators, particularly the Rf and Rg color rendering indices:

1. Preference (P): Comprehensive Consideration of Visual Pleasure and Naturalness

The Preference category requires Rf color rendering index (global fidelity) ≥78, Rg color rendering index (gamut index) ≥95, while limiting red region chroma shift (Rcs,h1) between -1% and 15%. In the IES TM-30-24 standard, Rf and Rg color rendering indices are the core parameters for evaluating the Preference category. For example, museum lighting may prioritize P1 level light sources to balance realism with visual appeal.

• P1 Level: Rf color rendering index ≥78, Rg color rendering index ≥95, Rcs,h1 between -1% and 15%, suitable for scenarios requiring balance between realism and visual appeal.
• P2 Level: Meets partial requirements of P1 level, suitable for lighting scenarios with certain requirements for visual pleasure.
• P3 Level: Meets basic preference requirements, suitable for general lighting applications.

2. Vividness (V): Focus on Color Saturation Enhancement Effects

The Vividness category focuses on color saturation enhancement effects. V1 level requires Rg color rendering index ≥118 and Rcs,h1 ≥15%. In the IES TM-30-24 standard, Rg color rendering index is the key indicator for evaluating Vividness, suitable for retail display and other scenarios requiring enhanced color performance.

• V1 Level: Rg color rendering index ≥118 and Rcs,h1 ≥15%, suitable for retail display, product display, and other scenarios requiring enhanced color performance.
• V2 Level: Meets partial requirements of V1 level, suitable for scenarios with certain requirements for color saturation enhancement.
• V3 Level: Meets basic vividness requirements, suitable for scenarios requiring moderate color saturation enhancement.

3. Fidelity (F): Emphasis on Color Reproduction Accuracy

The Fidelity category emphasizes color reproduction accuracy. F1 level requires Rf color rendering index ≥95, and red region local fidelity (Rf,h1) ≥90. In the IES TM-30-24 standard, Rf color rendering index is the core indicator for evaluating Fidelity, suitable for medical surgery and other environments with extremely high requirements for color accuracy.

• F1 Level: Rf color rendering index ≥95, and Rf,h1 ≥90, suitable for medical surgery, precision manufacturing, and other environments with extremely high requirements for color accuracy.
• F2 Level: Meets partial requirements of F1 level, suitable for scenarios with high requirements for color reproduction accuracy.
• F3 Level: Meets basic fidelity requirements, suitable for general color reproduction needs.

4. Performance Level Representation Method

When a light source's performance does not meet the minimum priority (Level 3) requirements, it is represented by "-", such as "V-" indicating that the light source does not meet the minimum vividness requirements. This representation method clearly shows the performance level of light sources in different design intent categories, helping lighting designers select appropriate light sources based on specific application scenarios.

II. Quantitative Breakthrough in Local Color Performance

IES TM-30-24 introduces local chroma shift (Rcs,h1) and local fidelity (Rf,h1), achieving fine-grained evaluation of specific color regions for the first time, which is an important breakthrough in the IES TM-30-24 color rendering index evaluation system. Rf and Rg color rendering indices serve as the foundation evaluation indicators, working together with local parameters to form a complete evaluation system.

1. Rcs,h1: Red Region Chroma Shift Index

Rcs,h1 is the only color rendering index indicator that quantifies red region saturation changes, used to quantify the chroma (saturation) changes of light sources in the first hue bin (red region). In lighting design, it is a key tool for balancing realism and visual appeal.

• Positive Value: Indicates red region chroma enhancement (more vivid), suitable for scenarios requiring enhanced red performance.
• Negative Value: Indicates chroma reduction (more dull), suitable for scenarios requiring reduced red saturation.
• Zero Value: Indicates red region chroma is the same as the reference light source.

The Rcs,h1 color rendering index parameter provides lighting designers with the ability to precisely control red region color performance, with important application value especially in retail, dining, and other scenarios requiring emphasis on red products or food.

2. Rf,h1: Red Region Local Fidelity Index

Rf,h1 is a local fidelity color rendering index indicator used to quantify the color reproduction capability of light sources in the first hue bin (red region).

• Rf: Global fidelity index (reflecting the average color rendering fidelity of all color samples), one of the core color rendering indices of the TM-30 standard.
• h1: "h" represents hue, "1" represents the first hue bin (based on 22.5° hue circle division, usually corresponding to the red region of 0°±11.25°).

The Rf,h1 color rendering index parameter enables the TM-30-24 standard to evaluate the fidelity of light sources to specific color regions, which is of great significance for medical, printing, and other application scenarios with extremely high requirements for specific color accuracy.

III. Optimization and Extension of Basic Color Rendering Indices

1. Evolution of Fidelity Index (Rf)

The Rf color rendering index is a core evaluation indicator in the IES TM-30-24 standard, measuring the overall color rendering fidelity of light sources to 99 color samples, still calculated based on the CAM02-UCS color space, but by introducing a brightness adaptation model, it corrects color perception differences at different brightness levels. Rf color rendering index, together with Rg color rendering index, forms the foundation evaluation system of the IES TM-30-24 standard.

• Range: 0-100, higher values indicate color reproduction closer to the reference light source, 100 being perfect match.
• Improvement: TM-30-24 enables the Rf color rendering index to accurately reflect color fidelity at different brightness levels by introducing a brightness adaptation model, which is an important improvement over the TM-30-18 standard.
• Application: The Rf color rendering index is a fundamental indicator for evaluating light source color reproduction capability, widely used in color quality evaluation for various lighting scenarios.

2. Extension of Gamut Index (Rg)

The Rg color rendering index is another core evaluation indicator in the IES TM-30-24 standard, quantifying the ratio of light source gamut area to reference light source gamut, reflecting overall color saturation changes. In the IES TM-30-24 standard, the upper limit of the Rg color rendering index has been raised from 100 to 140, allowing quantification of light source enhancement capabilities for color saturation. Rg color rendering index, together with Rf color rendering index, provides comprehensive color quality evaluation capabilities for the IES TM-30-24 standard.

• Rg>100: Indicates light source enhances color saturation, suitable for scenarios requiring enhanced color performance.
• Rg=100: Indicates light source gamut is the same as reference light source, with moderate color saturation.
• Rg<100: Indicates saturation reduction, insufficient color saturation.
• Upper Limit Increase: TM-30-24 raises the upper limit of the Rg color rendering index from 100 to 140, enabling the standard to quantify high saturation light source performance, which is of great significance for retail, display, and other application scenarios requiring strong color performance.

3. Upgrade of Color Vector Graphic (CVG)

The Color Vector Graphic (CVG) is an important tool in the IES TM-30 standard for visualizing color quality. IES TM-30-24 has made important upgrades to CVG, adding local offset arrows that can intuitively display the direction and magnitude of chroma changes for each hue bin, while clearly showing the evaluation results of Rf and Rg color rendering indices.

• Global View: Displays overall chroma change trends for all color samples.
• Local Offset Arrows: New feature that can intuitively display the direction and magnitude of chroma changes for each hue bin (such as red region h1), helping designers quickly identify performance in specific color regions.
• Application Value: The upgraded CVG makes TM-30-24 color rendering index evaluation more intuitive and practical, especially suitable for lighting design scenarios requiring fine control of specific color region performance.

IV. Application Value of TM-30-24 Color Rendering Index Evaluation Method

The IES TM-30-24 Method for Evaluating Light Source Color Rendition provides more precise and practical color quality evaluation tools for the lighting industry by introducing a three-dimensional evaluation framework and local color performance quantification indicators. The IES TM-30-24 standard, with Rf and Rg color rendering indices as the core, offers the following main advantages:

1. Design Intent Orientation: Through P, V, F three categories, color rendering index evaluation can directly match actual lighting design needs.
2. Local Fine-Grained Evaluation: Through local color rendering index parameters such as Rcs,h1 and Rf,h1, precise control of specific color regions is achieved.
3. Indicator Optimization and Extension: The brightness adaptation improvement of the Rf color rendering index and the increase in the upper limit of the Rg color rendering index make the evaluation system more complete.
4. Visualization Enhancement: The CVG upgrade makes color quality evaluation results more intuitive and understandable.

V. Summary

The IES TM-30-24 Method for Evaluating Light Source Color Rendition represents the latest progress in the field of color quality evaluation. By introducing a design intent-oriented three-dimensional evaluation framework and local color performance quantification indicators, it provides lighting designers with more precise and practical color rendering index evaluation tools. Key parameters in the IES TM-30-24 standard, such as Rf color rendering index, Rg color rendering index, Rcs,h1 color rendering index, and Rf,h1 color rendering index, provide scientific basis for color quality evaluation in different application scenarios. Among these, Rf and Rg color rendering indices are the core evaluation indicators of the IES TM-30-24 standard, widely used in color quality evaluation for various lighting scenarios.

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