TM-30 and SDCM

What is TM-30?

The IES TM-30 is a color rendering evaluation method introduced by the Illuminating Engineering Society (IES) in 2015 to overcome the limitations of the traditional Ra (CRI) metric. TM-30 offers a more comprehensive and accurate approach to assessing the color rendering performance of a light source, providing a much deeper insight than conventional indices like Ra.
Unlike CRI, which only uses 8 color samples, TM-30 evaluates 99 color samples—resulting in a more robust and realistic assessment of how a light source renders colors.

Color Fidelity Index (Rf)
The Rf measures how accurately a light source reproduces colors compared to a reference light source—similar to the CRI method but using TM-30’s expanded 99 color samples. A higher Rf score indicates better color accuracy, with a perfect score of 100 representing a light source that renders colors identically to the reference source.

Gamut Index (Rg)
The Rg measures the saturation of colors rendered by a light source compared to a reference. It provides valuable information about the intensity and vibrancy of colors.

🔹Rg = 100: Matches the reference source’s color saturation

🔹Rg > 100: Indicates oversaturation (colors appear more intense)

🔹Rg < 100: Indicates desaturation (colors appear more muted)

Together, Rf and Rg provide a complete picture of a light source’s color performance, with Rg adding valuable information on color vividness and intensity.

Color Vector Graphic
While Rf and Rg provide numeric values, the Color Vector Graphic gives a visual representation of color saturation differences.

🔹Black circle = Reference light

🔹Red shape = Test light

🔹Red lines inside the black circle = Desaturation of those hues

🔹Red lines outside the black circle = Oversaturation of those hues

🔹Overlapping lines = No change; hues are rendered the same

What is SDCM (Standard Deviation Color Matching)?

SDCM has the same meaning as a MacAdam ellipse. It’s a unit used in lighting to describe how much a color deviates from a reference color. SDCM defines a zone in the CIE (x, y) color space within which people can perceive color variations at a given color temperature.

The American standard ANSI C78.376-2014 specifies reference points and sizes for six MacAdam ellipse sets, each corresponding to a specific color temperature.

The higher the SDCM number, the greater the color deviation and the more noticeable the difference. Conversely, a lower SDCM number indicates a smaller, less perceptible color shift.

In simple terms:

🔹1 SDCM: No visible color difference

🔹2–3 SDCM: Barely noticeable

🔹4+ SDCM: Clearly noticeable

Rf-Rg Plot Graph
This plot simply graphs Rf against Rg, offering a clear visual comparison of color rendering quality across different light sources. It’s a practical and insightful tool for evaluating and selecting lighting.