Achieving Optimal Color Rendition with LEDs

Overview

This white paper explains color rendering—how light affects the appearance of the colors we see. It describes various systems used for measuring the color rendition capability of light sources, such as the Color Rendering Index (CRI), Gamut Area Index (GAI), TM-30, and more. We compare these methods and discuss how they have evolved to provide more accurate assessment of LEDs for different lighting needs.

By properly applying these indices, you can create the right lighting scheme for virtually every type of environment—from retail stores to surgical operating rooms. The paper describes the superior color rendition capabilities of Luminus LED products and how they help architects and lighting designers meet specific functional lighting objectives.

Color Rendition

Color rendition (also commonly referred to as color rendering) is the effect of light on the color perception of objects. The International Commission on Illumination (CIE) defines color rendering as the "effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant."

Key concepts in understanding color rendition include:

• Human Color Perception: Humans see color when light enters the eye and strikes the retina, which contains color-sensitive cones that communicate with the brain.
• CIE Color Space: A mathematical system defined in 1931 to quantify all colors perceivable by the average human eye.
• Spectral Power Distribution (SPD): The wavelength profile of a light source that significantly affects environmental appearance and visual experience.
• Color Attributes: Fundamental characteristics including hue (specific color), value (lightness/darkness), and chroma (intensity/saturation).

Application Areas

Accurate color rendering matters in many industries and applications. Poor color rendering can make objects look unappealing, detract from an environment's ambiance, or make performing tasks difficult or unpleasant.

Retail Lighting

Retailers have unique lighting needs where considerations often include not only color accuracy but also enhancement. The goal is not necessarily "perfect" color rendition but creating an "exciting" visual appearance with vivid colors that draw consumers' attention and increase product appeal.

Hospitality Lighting

Hospitality venues such as hotels, restaurants, and bars have complex lighting needs. Different spaces require different approaches—lobby lighting should create warmth, while restaurant lighting must ensure food looks appealing. Decorative lighting can also be part of the mix to spotlight architectural features or artwork.

Medical Environments

In medical facilities, accurate color rendering is critical. Surgical operating room lighting must ensure surgeons can discern fine gradations of red tones to differentiate tissues, blood, and bodily structures. Lighting for this environment requires careful balance of color temperature and CRI considerations.

Specialty Environments

Other specialized applications include:

• Food Safety Lighting: Regulations require lighting that enables clear viewing for contamination detection, with particular emphasis on red wavelength rendering.
• Gallery/Museum Lighting: Requires high color fidelity while protecting artwork from damaging UV wavelengths.
• Stage Lighting: Uses color for emotional effect, enhancing skin tones, enlivening costumes, or changing scenery appearance.
• Video Lighting: Must account for how objects are captured by camera sensors and then perceived by human audiences.

Color Rendition Models

Various models exist to describe color rendition capabilities of light sources. These models typically characterize one of three key aspects: color fidelity (accurate rendition), color preference (pleasant, vivid appearance), and color discrimination (ability to distinguish between colors).

Color Rendering Index (CRI)

The CRI measures how accurately a light source can reveal color. It compares the appearance of eight defined Test Color Samples under a real light source against how they would look under a reference illuminant. CRI is reported as Ra, the average of samples R1-R8.

While widely used, CRI has limitations:

• Based on only eight color samples, which are considered limited and too pastel
• Developed before LED commercialization, potentially less accurate for LEDs
• Doesn't account for human perceptual preferences for vividness
• Can produce inconsistent results between devices with similar Ra values

Gamut Area Index (GAI)

GAI presents an alternative option for determining color perception under LED lighting. It measures hue saturation and can be used in combination with CRI. GAI values can exceed 100, with higher values indicating greater color saturation and differentiation.

Experts suggest that GAI (characterizing saturation/intensity) and CRI (characterizing chromatic accuracy) complement each other. Used together they provide a more complete method of evaluating a light source.

ANSI/IES TM-30

TM-30 represents the latest method for evaluating color rendering of LED light fixtures. A key differentiator is its use of 99 color samples instead of CRI's 8 samples. TM-30 provides two main metrics:

• Rf (Fidelity): Measures similarity to reference, analogous to CRI
• Rg (Gamut): Describes saturation level, analogous to GAI

TM-30-20 introduced design "intents" to help balance considerations:

• Color Preference (P): Intent to create a pleasing, natural-looking environment
• Color Vividness (V): Intent to create a vibrant scene
• Color Fidelity (F): Intent to achieve similar color appearance to reference illuminant

Each design intent includes three priority levels indicating the stringency of criteria, helping designers make informed trade-offs between different color rendition objectives.

Luminus Solutions for Accurate Color Rendering

Luminus LED products score well on both CRI and TM-30 rendering scales, offering architects and designers multiple options for accurate color rendering in different settings.

Standard LEDs (AccuWhite™)

The Luminus Standard LEDs (AccuWhite series) offer high-fidelity color rendering with consistent Ra = 97 CRI and minimum score of 93 across all hue angle bins. These products are available with standard warm white (2700K and 3000K CCT) and Candle Warm options (2200K and 1800K CCT).

Sensus™ for Superior Retail Lighting

Luminus Sensus LEDs provide consistent bright whites and pure colors, with 90+ CRI, Rf of 93 and Rg of 102 at 3000K. Unlike most retail lighting LEDs, Sensus products provide vivid whites and colors without using near-UV wavelengths to excite brightening agents.

PerfectWhite™ LEDs

Luminus PerfectWhite LEDs deliver near-perfect color rendering, ideal for specialty retail, luxury hospitality, museum, and art gallery applications. PerfectWhite bulbs provide an average (Ra) of 93 across the 15 CRI samples, and TM-30 scores of Rf = 92, Rg = 100.

Salud™ LEDs

The Salud line of LEDs is designed to achieve human-centric (circadian) lighting design objectives while providing exceptional color rendering accuracy. They achieve CRI Ra 90+ with high R9 reds.

Hospitality COB Series™ LEDs

Luminus Hospitality COB Series LEDs provide a warm, welcoming glow with pure whitening for high-fidelity color rendering (CRI of 90 and above), ideal for hotels, restaurants, and other hospitality venues.

Color Mix Tunable LEDs

Tunable LEDs are a recent development that allows users to adjust light characteristics. Luminus provides tunable Color Mix LEDs that can be adjusted across a range of SPDs to provide either cool white or warm white lighting. These products enable full control of each channel independently for customized lighting environments.

Conclusion

The color rendition performance of artificial light sources such as LEDs determines how well humans can perceive the world indoors and at night. Light sources with good color rendition are said to have high fidelity—they render people, objects, and environments accurately to our eyes.

For some lighting applications, fidelity is the most important quality. For others, considerations such as saturation, hue, or efficiency may be more important. By understanding and applying the various models of color rendition, we can determine which light sources create optimal viewing conditions for different applications—from retail stores to food processing plants, living rooms to hospital operating rooms.

While each color rendition model offers valid means of evaluating LED characteristics, combining several methods—such as CRI plus TM-30—can provide the most complete reference point for architects and lighting designers.

With their consistently high performance across all measures of color rendition and efficacy, Luminus LEDs offer solutions for virtually any color-sensitive lighting application.

Appendices

The complete white paper includes detailed appendices with:

• Appendix A: Measures and graphics included in ANSI/IES TM-30-18 reports
• Appendix B: Color rendition specifications and regulatory requirements
• Appendix C: Complete color rendering data for Luminus LED product lines