CRI & Color Rendering Guide
Ra, R9 and TM-30 explained for procurement decisions.
1. Why it matters
Colour rendering describes how faithfully a light source shows the true colours of what it illuminates, compared with a reference (daylight or an incandescent). CRI (Ra) is the long-standing average metric; R9 and the newer TM-30 (Rf/Rg) fill the gaps it leaves. For retail, healthcare, print and food, colour rendering is not a nicety — it directly changes what customers see and buy.
2. CRI, R9 and TM-30 — what each covers
| Metric | What it measures | Read it when |
|---|---|---|
| Ra (CRI) | Average fidelity across 8 pastel samples (R1-R8) | Always — the baseline |
| R9 | Saturated red rendering (weak spot of Ra) | Skin, meat, print, wood |
| Rf (TM-30) | Fidelity over 99 samples | Critical/specification work |
| Rg (TM-30) | Saturation (gamut) vs reference | Retail vibrancy tuning |
3. Match the target to the application
Higher CRI usually costs a few percent in efficacy (lm/W), so specify what the space needs rather than the maximum. General commercial work is fine at Ra 80; anywhere colour judgement matters wants Ra 90+ and a healthy R9.
- Warehouse / industrial: Ra 70-80 is acceptable, efficacy first.
- Office / education: Ra 80+ (many specs now ask 90).
- Retail / hospitality: Ra 90+, R9 > 50.
- Healthcare / print / art: Ra 95+, R9 > 90, check TM-30.
4. Colour consistency: don't forget MacAdam
A single high CRI number says nothing about whether two fixtures on the same ceiling match. Colour consistency is measured in MacAdam ellipses (SDCM): specify ≤ 3 SDCM for premium retail and ≤ 5 SDCM for general commercial, or you will see visible tint differences between adjacent units even at Ra 90. Also fix the CCT (e.g. 4000K) and require it be held across the batch.
5. Checklist
- Always read R9, not just Ra
- Specify Ra 90+ / R9 > 50 for retail and hospitality
- Ask for TM-30 Rf/Rg on colour-critical projects
- Set a MacAdam SDCM limit (≤3 premium, ≤5 general)
- Fix the CCT and require batch consistency