A new color quality evaluation method of the "5 changes" by North American Institute of illumination

Looking forward to the next in the lighting industry, lighting society of North America (IES) finally in May 18, 2015 in two years of work after the official release for the new evaluation method of color rendering of light sources -- IES TM-30-15 IES Method for Evaluating Light Source Color Rendition.

This new evaluation system by IES quality working group (IES Color color Metrics Task Force) is proposed, the working group consists of 8 members: Dr. Royer Mike (Pacific Northwest National Laboratory), Dr Ohno Yoshi (US NIST), Dr Houser Kevin (Penn State University), Dr Wei Minchen (Penn State University) Dr. Fini, Paul (CREE), Aurelien David (Soraa), Kees, Teunissen, and Randy Burkett (Philips) (US Randy Burkett lighting design firm).

Figure: TM-30-15 color evaluation system of the IES color quality working group members

The document was approved by the IES color Committee, the technical review board and the board of directors.

Compared with the existing CIE color index CRI, the new evaluation method of IES has the following 5 major changes:

1, two indicators: evaluation of light source color is no longer just use an indicator, but by the two indicators - Rf and Rg.

The Rf is used to characterize the similarity between the standard colors and the reference light source under the test light source (100 represents the same); the difference between the 0 is very large.

Rg represents the standard color saturation compared with a reference light source in the test change light source (representing 100 of the same saturation is greater than 100, said light source can improve the color saturation, color saturation is less than 100 in the test under low light).

Figure: color fidelity Rf and color saturation Rg

Figure: color fidelity index Rf (source: CREE)

Figure: color saturation index Rg (source: CREE)

2, standard color: compared with CRI only 8 standard color, the new system uses 99 standard colors. These 99 standard colors are no longer a dream Searl color card, but from the color of the 105000 objects carefully selected. They represent the common life can see various colors (from saturated to unsaturated, from light to dark), and the 99 standard color for each wavelength sensitivity (the same is very difficult by the gaming to improve the spectral index).

Figure: CRI uses 8 standard color R1-R8

Figure: IES TM-30-15 using 99 standard colors, from the color of the 105000 objects carefully selected, representing the common colors can be seen in life (from saturated to unsaturated, from bright to dark)

Fig. 99 spectral reflectance distribution curves of the IES standard colors

3, the reference light: as the reference light source used by CRI (i.e. less than 5000K when using blackbody radiation; above 5000K using natural light model) mutations of 5000K, this new system is in the range of 4500K-5500K using the blackbody radiation and natural light model of hybrid optical spectrum as the reference light source. In addition, both Rf and Rg use the reference light source with the same color temperature of the source to be measured, thus overcoming an important drawback of GAI.

4, colorimetry: the system uses a more uniform color space, color adaptation equation and color appearance model (CIE Color Appearance Model 02).

5, color: icon distortion due to the 2 comprehensive evaluation index can only source for a variety of colors of the average color, for certain color color capability are important sometimes (especially for the lighting designer). The new method also provides a color distortion icon to provide a more intuitive information, which can be used to represent the color drift and saturation of various colors.

Figure: can be more intuitive to express a variety of colors, color drift and saturation change color distortion Icon

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