The Relationship Between Display Color Temperature and Chromaticity Coordinate

To measure backlight color data of displays, we often encounter the terms "color temperature" and "chromaticity coordinates."

1. What is Color Temperature?

Color temperature is a physical quantity that measures the "warmth" or "coolness" of a light source's color, expressed in **Kelvin (K)**.

- At lower temperatures (e.g., 2000K–3000K), the light appears **orange-yellow** (warm), giving a cozy, soft feel.
- At mid-range temperatures (5500K–6500K), the light resembles **noon daylight** (neutral white).
- At higher temperatures (7500K–9300K and above), the light appears **bluish-white** (cool), giving a crisp, bright feel.

2. What are Chromaticity Coordinates?

Chromaticity coordinates are a pair of values ,(x, y) that precisely locate a color on the CIE 1931 chromaticity diagram (a color space standard established by the International Commission on Illumination).

- The CIE chromaticity diagram is a horseshoe-shaped representation of all colors visible to the human eye.
- Every point on this diagram represents a specific color, uniquely identified by its (x, y) coordinates.
- Every color produced by a display—white, red, green, blue, etc.—can be precisely described using chromaticity coordinates.

For example, the standard D65 white point has chromaticity coordinates of approximately **(x=0.3127, y=0.3290)**.

Chromaticity coordinates are a two-dimensional absolute coordinate system capable of precisely describing any color, whereas color temperature is merely a single-value parameter along one specific trajectory within this coordinate system.

## Part Two: The Relationship – Color Temperature as a "One-Dimensional Projection" of Chromaticity Coordinates

- Chromaticity coordinates (x, y)** are two-dimensional—they can describe any color anywhere on the chromaticity diagram.
- Color temperature (K) is a one-dimensional value that is only defined when a color's coordinates fall exactly on the Planckian locus, and its value equals the temperature at that point on the locus.

3. For Quality Control / Manufacturing: Both Coordinates and CCT are Required

On display production lines, quality standards typically specify both:

- CCT target (e.g., 6500K ± 500K): ensuring the overall warm/cool tendency falls within an acceptable range.
- **Chromaticity coordinate tolerances (e.g., x ≤ 0.005, y ≤ 0.005): ensuring the white point is pure, without green or purple tints.

Controlling color temperature alone cannot detect tint issues; controlling coordinates alone would be overly strict and reduce production efficiency. Combining both is the most scientifically sound approach to quality control.