CRI 90 is not good enough, and R9 is the reason
Devang M.
Head of Optical Engineering
The general index averages eight pastel test colours and quietly ignores saturated red. Two fixtures can both claim 92 CRI while one makes teak look like cardboard. Here is how we measure and specify what actually matters.
When an architectural specifier writes 'CRI > 90' into a tender document, they usually believe they have protected their project from dull, lifeless color rendering. In reality, the traditional CIE Ra index was defined in 1974 using eight low-chroma pastel swatches (R1 through R8). It completely omits R9 — the metric for saturated red.
The R9 Disconnect in Luxury Architecture
Natural timber like Burma teak, walnut veneers, warm Italian marble with terracotta veining, and human skin tones all rely fundamentally on the deep red portion of the visible spectrum (620nm–700nm).
A standard phosphor LED chip can score an average Ra of 91 while having an R9 value as low as 12. Under such light, expensive polished hardwood looks washed-out and greyish-brown.
- General Ra (CIE 1974)
- > 97.2
- Saturated Red (R9)
- > 92.0
- Skin Tone Fidelity (R13)
- > 98.4
- TM-30 Fidelity (Rf)
- 95+
- TM-30 Gamut (Rg)
- 101 (Natural vibrancy)
Why Red Phosphors Are Difficult & Expensive
Generating deep red wavelengths requires narrow-band potassium fluorosilicate (PFS) or nitride-based phosphors. These are physically more expensive to formulate and demand tighter thermal management on the COB copper substrate to prevent color shift at 65°C operating junction temperature.
Standard off-the-shelf commercial fixtures compromise on R9 to artificially inflate lumen-per-watt efficiency numbers. At Edison, we calibrate our custom COB engines for spectral completeness rather than raw lumen vanity.
Key Engineering Takeaways
- CRI (Ra) only measures R1–R8; R9 (saturated red) is excluded from the standard average.
- Teak, Italian marble, leather, and skin tones depend entirely on R9 > 85 for natural warmth.
- Always request TM-30-20 reports with Rf > 90 and Rg ~ 100 for luxury residential interiors.