The Technical Memorandum TM-30-18 describes a method that is an approved American National Standard to evaluate light source color rendition. The procedure uses an objective and statistical approach to quantifying the fidelity (closeness to a reference) and gamut (increase or decrease in chroma) of a light source.

The following section is dedicated to the aspects of chroma shift measures and luminous efficacy of radiation (LER).

To describe the chroma shifts in % all information about lightness and hue changes are discarded. A negative value for the local chroma shift indicates a decrease in chroma, whereas a positive value indicates an increase in chroma. The values are calculated for all 16 hue-angle bins to represent averaged samples for each bin.

The range of possible local chroma shift values varies with hue-angle bin. If all light sources among 212 commercially available and 14 788 theoretical SPDs selected that feature a Rf ≥ 70 the range is the following.

If no restrictions are made the possible shifts are considerable higher.

TM-30 is developed to evaluate aspects of light quality, energy efficiency was not a primary concern. In fact, it is acknowledged that including color samples with very long-wavelength or very short-wavelength components necessitates that a lamp include appropriate radiation in those regions, thus lowering the maximum luminous efficacy of radiation (LER) achievable with a perfect or near-perfect Rf value. A more limited color sample set would generally result in higher LER, but compromise information on color rendering characteristics.

It is responsibility of designers and planners to specify solutions that consider criteria as color quality, luminous efficacy, energy efficiency, cost, luminous intensity distribution, and appearance. Manufacturer are asked to provide products that fit given specifications.

Here are examples of color vector graphics for some light sources.

Links to additional information and resources about IES TM-30-18

Free download of the ANSI/IES  TM-30-18

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