CRI and TM-30 — How Color Rendering Affects Indoor Lighting and What to Specify

Quick Answer

CRI alone tells you almost nothing useful — R9 (saturated red) and TM-30's Rg (gamut index) are where the real problems hide. A fixture labeled "CRI 90" can make fresh beef look grey and human skin look pallid if R9 is low. Always ask for R9 and TM-30 data before accepting any CRI spec.

CRI measures how accurately a light source renders eight standard color samples (R1–R8) compared to a reference light. The average is Ra — that's the number on the datasheet. But those eight samples are all pastels. Saturated red, saturated blue, skin tones, green foliage — all missing. That's why CRI 90 can still look terrible [LED Magazine Lab Test 2024, Sample=12 fixtures].

What does this actually look like? Under a CRI 80 fixture, a cut of fresh beef looks brownish-grey. The surface looks dry, not appetizing. Under a CRI 90 fixture with R9 > 50, the same beef looks red and moist — the surface looks like it was just cut. Swap in a CRI 90 fixture where R9 = 10, and you're back to grey-beef territory, despite the "90" on the label. R9 is the difference between product that sells and product that sits.

TM-30 — The New Standard

IES TM-30-23 (IES Method for Evaluating Light Source Color Rendition) addresses CRI's known limitations: insufficient color samples, no saturation information, and poor correlation with visual perception.

Two products with the same CRI 90 can have Rg values of 95 (slightly washed out) and 105 (vibrant). Stand them side by side and the difference is obvious. CRI can't tell you which is which [LED Magazine Lab Test 2024, Sample=12 fixtures].

📊 CRI (Ra) vs TM-30 Rf vs TM-30 Rg — At a Glance

Application-Specific Recommendations

Common Mistakes

Specifying "CRI > 80" for a supermarket deli counter. That's the mistake that costs you sales. CRI 80 is fine for a corridor. For the deli, bakery, or fresh meat case — you need CRI > 90 and R9 > 80. Anything less and the product looks old before it is.

Using CRI without R9. A fixture with Ra 90 and R9 = 10 exists in the market and is cheap. It makes reds look brown. Always add "R9 > 50" (or higher for food retail) to your specification.

Not asking for TM-30 when comparing two CRI 90 options. Two panels, both CRI 92. One has Rg 98, the other has Rg 103. The visual difference is immediate in a side-by-side install. Test them if you can.

Key Takeaways

• R9 (saturated red) is the most important single number on any LED datasheet — CRI's eight pastel samples don't catch red rendering problems
• Two "CRI 90" fixtures can look completely different; R9 and Rg (gamut index) tell you which is which
• For fresh food retail: specify CRI > 90 + R9 > 80 minimum, or your meat looks grey
• Always request R9 and IES TM-30-23 data — if the supplier only gives you "CRI > 80," they're hiding something

❓ Frequently Asked Questions

Q: When should I use TM-30 instead of CRI?

A: Use TM-30 whenever color appearance directly impacts business outcomes — retail displays, fresh food counters, art galleries, medical examination rooms, and high-end hospitality. CRI alone is acceptable only for general-purpose spaces (corridors, warehouses, parking) where color accuracy is not critical. For any spec where you're comparing two "CRI 90" products, TM-30 reveals the real differences that CRI masks.

Q: What Rf/Rg values are considered good?

A: Rf ≥ 85 is the baseline for "good" color fidelity in most applications. Rf ≥ 90 is excellent and recommended for color-critical tasks. Rg 95–105 indicates near-neutral saturation; Rg 100–110 is often preferred in retail to make products appear more vivid. Avoid Rg < 90 (visibly washed out) and Rg > 115 (oversaturated, unnatural) unless intentionally designing for effect.

Q: How does TM-30 affect retail sales and customer perception?

A: TM-30's Rg (gamut) directly impacts how products look to customers. An Rg of 100–105 makes fabrics, produce, and merchandise appear vibrant without looking artificial. Studies show that lighting with higher Rg values (within the 100–110 range) increases perceived product quality and purchase intent in retail environments. Conversely, Rg below 95 makes colors look dull and can reduce perceived value — even if CRI is 90+.

Q: Does TM-30 replace CRI?

A: Not yet — TM-30 complements CRI rather than replacing it. CRI (Ra) remains the most widely quoted metric on datasheets and in procurement specifications. However, IES TM-30-23 is increasingly required in North American lighting specifications for color-critical applications. The smart approach: specify both CRI ≥ 90 and request TM-30 reports. Over time, TM-30 is expected to become the primary standard as adoption grows.

Q: What's the difference between TM-30-18 and TM-30-23?

A: TM-30-23 is the latest revision (2023) of the IES standard, replacing TM-30-18. Key updates include refined calculation methods, improved correlation with visual perception, and additional Annexes for application-specific guidance. Always reference TM-30-23 in new specifications.

Q: How do I read a TM-30 Color Vector Graphic?

A: The graphic shows 16 hue bins arranged in a circle. Arrows pointing outward indicate oversaturation in that hue; arrows pointing inward indicate undersaturation. A perfectly neutral light would show all arrows at the reference circle. For retail, look for arrows pointing slightly outward in red and warm tones — this enhances product appeal. Avoid large inward arrows in any hue, which indicate color dulling.

Q: Can you get CRI 90 without sacrificing lumens per watt?

A: Yes, with the right chip. Premium manufacturers (Nichia, Lumileds, Seoul Semiconductor) now hit CRI 90+ at 130–150 lm/W in mid-power packages. The trade-off only gets painful at CRI 97+ with R9 > 95 — then you're looking at 10–15% more power for the same output [LED Magazine Lab Test 2024, Sample=12 fixtures].

Q: Does CRI matter for outdoor lighting?

A: Less so for parking lots and streets where visibility and uniformity are the priorities. But for outdoor restaurant terraces, hotel entrances, or retail signage, go with CRI > 80 and R9 > 30 — your guests and customers will notice the difference.

Q: How do I verify the standards cited in this article?

A: IES TM-30-23 (Color Rendition Method) can be accessed at store.ies.org. IEC 60079 (for explosive atmospheres in Article 7) at webstore.iec.org. IES standards: store.ies.org.

✅ Specifier Checklist — When to Require TM-30 Reports

Use this checklist when writing lighting specifications or evaluating supplier proposals. Request full TM-30-23 reports (not just summary values) whenever any of the following apply:

Pro tip: Add language to your spec: "Supplier shall provide IES TM-30-23 test reports including Rf, Rg, and Color Vector Graphic for the specified CCT(s). Reports must be from an ISO 17025-accredited laboratory. Summary values or catalog claims alone are not acceptable."

Related Questions

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