CRI, R9, TM-30: How to Read Light Quality Specs

Color quality is the most consequential and least understood dimension of lighting specification. A fixture that produces the right lumens, the right beam angle, and the right CCT can still make an $80,000 kitchen look cheap if its color rendering is poor. CRI, R9, and TM-30 are the three metrics that determine whether the marble looks like marble, the wine looks like the wine, and the occupant looks healthy. Here is how to read them.

What Is CRI?

Color Rendering Index (CRI) is a 0–100 scale that measures how accurately a light source renders a set of standardized test colors compared to a reference illuminant (typically a blackbody radiator at the same color temperature). The test set consists of 8 “Munsell” color samples, designated R1 through R8. Each R-score measures how closely the test source reproduces that specific color versus the reference; the arithmetic average of R1–R8 is the CRI value you see on a spec sheet.

A CRI of 100 means the source renders all 8 test colors identically to the reference. A CRI of 80 means average rendering fidelity across the 8 samples, with individual samples potentially worse. For luxury residential applications, CRI 90 is the minimum acceptable specification. CRI 95+ is the specification for spaces where color accuracy is critical: galleries, dressing rooms, kitchen preparation areas.

Why CRI Is Not Enough: R9

The eight standard CRI test samples (R1–R8) are moderate-saturation, relatively unsaturated colors. They exclude a critically important real-world color: saturated red. Saturated red. test sample R9. is the color that most distinguishes excellent LED sources from mediocre ones, and it is explicitly excluded from the CRI average.

A fixture can achieve CRI 90 while scoring R9 below zero. Negative R9 means the fixture actively distorts red hues. red wine looks brownish, skin tones look sallow, warm-toned artwork appears muted. This is why many CRI 90 LED installations look “off” compared to incandescent: the R9 score is poor.

Minimum specification: R9 > 50 for general residential lighting. R9 > 80 for spaces with fine art, wine display, or where skin tone rendering is important. Most premium LED downlight manufacturers (including those carried by Restrepo Innovations) achieve R9 80–98 alongside CRI 90–95+.

TM-30: The Better Standard

The Illuminating Engineering Society (IES) published TM-30. the IES Method for Evaluating Light Source Color Rendition. as a more comprehensive alternative to CRI. Where CRI uses 8 test samples and produces one number, TM-30 uses 99 scientifically selected color samples representing real-world objects and produces two key metrics:

Rf (Fidelity Index): Analogous to CRI. how accurately the source renders colors compared to a reference. Scale of 0–100. Values above 78 are considered good; above 85 is excellent.

Rg (Gamut Index): Measures whether the source expands or compresses the color gamut compared to the reference. Rg = 100 means identical gamut. Rg > 100 means the source saturates colors slightly. which many lighting designers prefer for residential accent applications because it makes colors “pop.” Rg < 100 means color compression, which makes spaces feel flat.

A well-specified residential LED source for accent lighting might target: Rf 90+, Rg 100–107. This combination renders colors accurately while providing a slight saturation boost that makes the space feel vibrant without visual distortion. TM-30 data is available from premium manufacturers on request; if a supplier cannot provide TM-30 data, that is itself informative.

Reading the Spec Sheet: A Practical Guide

When evaluating a fixture for luxury residential specification, look for the following on the photometric data sheet:

CRI: Should be listed as ≥90 at the specified CCT. If only listed as a range (e.g., “CRI 80+”), request the specific value for the ordered CCT.

R9: May not appear on the main spec sheet. Request it explicitly. If the manufacturer cannot provide R9, assume it is poor.

TM-30 Rf and Rg: Available from premium manufacturers in their photometric data packages. The IES test report (LM-79) will reference TM-30 metrics on higher-tier products.

Spectral Power Distribution (SPD): The graph showing relative output at each wavelength. A smooth SPD without narrow spikes indicates a well-phosphor-converted LED that will render colors uniformly. Spiky SPDs indicate poor color rendering even if CRI appears acceptable.

Which Spaces Need the Highest Color Quality?

Not every space requires CRI 95 and R9 95. Utility spaces, garages, and storage areas can tolerate CRI 80. The investment in high-color-quality sources is concentrated where it has visual impact:

Must specify CRI 95+, R9 80+: Art display areas; primary kitchen lighting; master bathroom; wine cellar; dining room accent lighting; any space with significant red-toned materials (mahogany, leather, terracotta).

Should specify CRI 90+, R9 50+: Living rooms; master bedroom; home office; hallways and entry; outdoor accent uplighting.

CRI 80+ acceptable: Utility spaces; exterior perimeter security; garage.

For the full framework of how these color quality specifications integrate into a lighting design, see our luxury lighting design hub. For a discussion of how CCT interacts with CRI in circadian applications, see circadian lighting done right. For how these metrics inform RGBW and tunable white specifications, see tunable white vs RGBW vs RGBWW.