What’s the difference between color terminology like Hue, Value, and Saturation (Chroma)?

Certain terminology and core concepts are used to characterize different aspects of color appearance. Understanding these terms is vital for understanding the color rendition measurements of light sources and to design lighting that is optimal for different applications. These terms and concepts include: hue, saturation/chroma, chromaticity, gamut, fidelity, value, color preference, and chromatic fidelity.

• Hue refers to the specific color, for example, red, red-orange, and orange are three hues.
• Value refers to how light or dark a color a color is—how much gray is incorporated. Black has a low value (dark), white has a high value.
• Chroma refers to the intensity of a color, how pure its hue is. Also referred as saturation—highly saturated colors are vivid; low-saturation colors appear more washed out or dull. The colors along the edge of the CIE color space can be said to be fully saturated, as they are pure wavelengths of their respective colors. Highly saturated colors can also be described as high chroma.
• The color fidelity of a light source refers to how accurately it renders the color of an item compared to a reference source. The Color Rendering Index (CRI) is a measure of fidelity.
• Chromaticity describes the coordinates of a light source SPD on a diagram such as the CIE 1931. It represents a combination of wavelength and purity.

The terms defined above are all objective measures of light and color; they can be quantified based on physical properties such as wavelength distribution. The next two concepts describe subjective characteristics that relate to human perception:

• Color preference refers to the aesthetic qualities of a light source. Research demonstrates that human observers prefer colors that appear both “natural” and “vivid”. Color preference is an characteristic relevant to color gamut measurement.
• Chromatic adaptation is an aspect of human perception, where our visual system partially adapts to slight differences in the color and amount of light. For example, as light transitions from bluish daylight at noon to more amber in the afternoon, our eyes adjust so the color of objects will nevertheless appear constant. Similarly, artificial light that is slightly off-white will be perceived as a true white after some time lapse.

Color preference is just one of several subjective attributes of lighting. Even though CRI is referenced to human visual perception (the CIE color space), it is an objective metric. When designing lighting for human-occupied spaces, subjective attributes of color are also an important consideration. Based on various studies of human psychological response, we prefer lighting that renders objects and the environment with attributes such as naturalness and vividness. Other variants include normalness, acceptability, vibrancy, and appreciation.¹

To learn more, refer to the Help Center articles:

FAQ -> Color Quality Metrics

White Papers -> Achieving Optimal Color Rendition with LEDs

REFERENCE:

1. Royer, M., 2021. “Tutorial: Background and Guidance for Using the ANSI/IES TM-30 Method for Evaluating Light Source Color Rendition.” LEUKOS. Online before print.

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