How to Verify CRI Claims with an LM-79 Test Report

How to Verify CRI Claims with an LM-79 Test Report

Marketing copy can say “90+ CRI” all day. The only way to know what a luminaire really does is to read the LM‑79 report behind that claim.

This guide walks through, step by step, how to use an LM‑79 report to verify Color Rendering Index (CRI), R9, and related color metrics before you commit to a fixture—whether you are a contractor bidding a project, a facility manager defending a spec, or a DIYer upgrading a garage workshop.

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1. LM‑79 in One Page: What It Is and Why It Matters for CRI

LM‑79 is the Illuminating Engineering Society (IES) standard that defines how to measure optical and electrical performance of complete solid‑state luminaires—total lumens, efficacy (lm/W), CCT, CRI, power factor, and more. According to the ANSI/IES LM‑79‑19 overview, it also requires laboratories to state measurement uncertainty for key metrics.

For CRI verification, three points are critical:

• Whole-luminaire test, not bare LED
  LM‑79 is applied to the entire fixture as shipped—optics, diffuser, and driver included—not just the LED package. As highlighted in industry guidance on LM‑79 vs LM‑80/TM‑21 from Hi‑Tech LED, testing only a bare LED engine often overstates CRI because lenses or diffusers can alter the spectrum.

• Application-ready data
  LM‑79 produces the same data that DLC (DesignLights Consortium) and many utility rebate programs rely on, so it is the de‑facto “performance transcript” for a luminaire.

• CRI is not measured in the field
  There is no simple handheld tool on the jobsite that replicates a lab‑grade CRI measurement. You depend on the lab report and the lab’s accreditation.

Practical implication: If the color performance is important (retail aisles, QC inspection lines, automotive paint bays), do not accept a CRI claim without a matching LM‑79 report for the exact SKU you are buying.

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2. Checklist: Minimum Requirements for a Trustworthy LM‑79

Before you even look at the CRI number, confirm that the LM‑79 report itself is worth trusting.

2.1 Quick triage checklist

Use this as a first‑pass filter when a vendor sends you “LM‑79 data”:

1. Exact model identification

   • The report must list the full model number / SKU, including driver option, CCT, and any lens or reflector package (e.g., wide vs narrow beam).
   • If you see only a generic family code or just the LED module identifier, push back.

2. Whole luminaire, not just LED package

   • Somewhere near the front you should see a description like “UFO high bay, 150 W, 5000 K, clear lens, 120–277 V driver.”
   • If the description sounds like an LED board (“mid‑power SMD array, 48 V”), it is probably a component test, not LM‑79 on the finished luminaire.

3. Accredited laboratory

   • Look for a statement that the test lab is accredited (NVLAP, A2LA, or other ILAC MRA signatory) for LM‑79. The NVLAP directory lets you confirm that the lab’s scope explicitly includes LM‑79 testing.
   • If you cannot match the lab to NVLAP or an equivalent accreditation body, treat the report as a marketing document, not an acceptance test.

4. Standard version and method

   • The report should state LM‑79‑19 (the current revision) or at least LM‑79‑08.
   • It should specify whether a goniophotometer or integrating sphere method was used and whether the test was conducted in absolute photometry.

5. Test conditions clearly reported

   • Ambient temperature (typically 25 °C), input voltage (e.g., 120 V, 277 V), mounting orientation, and stabilization time must be stated.
   • If your installation runs hotter (e.g., a 40 °C factory), expect lower lumens and slight color shift compared with a 25 °C test; ask for “hot‑state” or elevated‑temperature data when color stability is critical.

6. Measurement uncertainty

   • LM‑79‑19 explicitly requires reporting measurement uncertainty for photometric and colorimetric data. The sample text in the LM‑79‑19 study guide shows CRI uncertainty commonly around ±1–2 points.
   • If the report omits any uncertainty statement, you can still use it for everyday projects, but for disputes or mission‑critical specs, treat it as incomplete.

2.2 What specifiers often miss

A frequent real‑world mistake is to accept a PR one‑pager (“CRI > 90, R9 > 50”) instead of the full LM‑79 PDF. Another is to use an LM‑79 for a 4000 K version to justify the 5000 K SKU. For rigorous projects, your purchase order should explicitly require:

• LM‑79 for the exact CCT and driver option you are buying.
• Lab accreditation evidence (e.g., NVLAP lab code) and test date.
• Access to the full spectral power distribution (SPD) data or at least a CSV export.

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3. Where to Find CRI Data in an LM‑79 Report

Once you trust the document, you can zero in on the color metrics.

Most LM‑79 reports follow a similar structure:

• Front page / summary table – headline metrics: lumen output, input power, efficacy, CCT, CRI (Ra), chromaticity coordinates (x, y or u′, v′), maybe Duv.
• Detailed color data section – table with CIE Ra, individual R1–R15 values, possibly R9 called out, plus CCT and Duv.
• Spectral power distribution graph – SPD curve showing radiant power vs wavelength.
• Optional TM‑30 section – TM‑30 fidelity (R_f) and gamut (R_g) values, color vector graphics.

According to the sample LM‑79 reports aggregated in industry libraries such as the RLUX shoebox example, the color table often looks like this:

Metric	Typical Label in LM‑79	What It Means
CRI (Ra)	“CIE General Color Rendering Index (Ra)”	Average rendering across 8 test colors; main marketing number.
R9	“Special Color Rendering Index R9”	Deep red rendering; critical for skin tones, food, branding.
CCT	“Correlated Color Temperature (K)”	Warm/cool appearance of the white light.
x, y	“Chromaticity Coordinates (CIE 1931)”	Exact point within the ANSI C78.377 chromaticity bin.
Duv	“Distance from Blackbody Locus”	Tint shift toward green (+) or magenta (–).

If your LM‑79 PDF only shows Ra and CCT with no R9 or SPD, treat the CRI number as a summary, not a full picture of color quality.

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4. How to Compare Catalog CRI vs LM‑79 CRI

4.1 Understand measurement tolerance

One of the most important nuances from LM‑79‑19 is that CRI is not an absolute truth. As discussed in the LM‑79‑19 commentary, typical accredited labs quote uncertainty on Ra of ±1–2 points. In practice:

• A product advertised as 90 CRI that tests at 88–89 is usually within normal measurement tolerance, not proof of misrepresentation.
• A discrepancy of 4–5 points (e.g., claimed 90, tested 85) is a red flag and justifies questions or retesting.

4.2 Pragmatic acceptance rules

Drawing on common practice and example reports such as the RLUX LM‑79 sample, a practical review rule set for most interior projects is:

• Ra within ±2 points of the catalog claim – typically acceptable.
• CCT within 100–150 K of the stated value – normal binning variation.
• R9 within about 5–10 points of whatever was shown in the product doc when high‑red rendering is part of the specification.

This matches the practitioner heuristic summarized in the research insight: for most interior work, small deviations in Ra and CCT are expected; the real concern is whether R9 and the full R1–R15 profile still support the application.

4.3 Case example: warehouse vs inspection line

• General warehouse (pallet racking, 30–50 fc)

  • Target: CRI ≥ 80, R9 ≥ 0.
  • If the catalog says CRI 82 and the LM‑79 shows Ra 81.0, CCT 4950 K, R9 –2, this is generally fine—binning and uncertainty cover the difference.

• Electronics repair benches or paint inspection line

  • Target: CRI ≥ 90, R9 ≥ 50.
  • If the spec calls for CRI 90 and the LM‑79 shows Ra 88.3, CCT 5100 K, R9 43, you have a decision: technically close, but several points short on both Ra and R9. For color‑critical work, it is usually safer to treat that as not meeting spec, or to update the spec to match what the fixture actually delivers.

If your projects focus heavily on the trade‑offs between 80 and 90 CRI in real spaces, you can go deeper with dedicated discussions such as the guide on CRI 80 vs. CRI 90 in retail lighting.

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5. Looking Beyond Ra: R9, R1–R15, and TM‑30

5.1 Why R9 matters more than many people think

A pervasive misconception in the field is that “if Ra meets the spec, the color will be fine.” The reality, as reflected in CIE 13.3 on color rendering and later research summarized by the CIE method for color rendering, is that a light source can meet the nominal Ra target while rendering reds, wood, or brand colors poorly.

R9 is the special test color for strong red. When R9 is low or negative:

• Meat and produce look dull.
• Skin tones look grayish or “sick.”
• Corporate reds and orange branding lose punch.

A strong expert consensus is:

• General warehouses, back‑of‑house: CRI ≥ 80, R9 ≥ 0 is usually enough.
• Retail sales floor, hospitality, healthcare, QC inspection: aim for CRI ≥ 90 and R9 ≥ 50.

The key point from the research insight is that matching Ra alone is not sufficient; uneven R1–R15 scores or weak R9 can make the space feel flat even at “90 CRI.”

5.2 Full R1–R15 profile

A solid LM‑79 report will list all R1–R15 values. When reviewing:

• Look for consistent scores, not just a headline Ra. A profile like R1–R8 around 90, but R9 = –5 and R12 (blue) = 60, indicates a lopsided spectrum.
• Check that values align with the intended use: wood shops benefit from strong R10/R11 (yellows and greens), fashion retail from strong R9, R13, and R15 (skin tones).

5.3 TM‑30: the next‑generation view of color

TM‑30 is a newer IES method that evaluates color rendition using fidelity (R_f) and gamut (R_g), plus a hue‑by‑hue graphic. As the TM‑30 standard explains, it offers a more nuanced picture than CRI, which can be fooled by spiky spectra.

Key TM‑30 metrics:

• R_f (fidelity): Similar to Ra but with more sample colors. Values near 100 mean faithful rendering.
• R_g (gamut): Indicates saturation. 100 ≈ neutral, >100 more saturated, <100 desaturated.

Some utility programs and institutional specs referenced by the DesignLights Consortium SSL technical resources have started to require minimum R_f and R_g thresholds, especially for high‑quality interior lighting. If your LM‑79 report does not include TM‑30 or spectral data to derive it, you may find a product quietly ineligible for certain rebates despite a strong CRI claim.

5.4 Pro Tip: When a lower CRI can look better

A counter‑intuitive but important insight from TM‑30 research is that a well‑balanced Ra 88 source with high R9 and R_g slightly above 100 can look better on faces and merchandise than a nominal 95 CRI product whose spectrum is spiky. As discussed in the TM‑30 documentation, preference and vividness are not perfectly captured by Ra alone.

For specifiers, this means:

• Do not chase the highest Ra number on paper; look for balanced R_f/R_g and healthy R9.
• In your specs, consider calling out minimum TM‑30 metrics, not just Ra, when color quality is central to the project.

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6. Verifying That the LM‑79 Actually Applies to Your Fixture

Even an excellent LM‑79 report is useless if it does not match the product you install. There are a few common failure modes that show up repeatedly in projects.

6.1 SKU mismatch and options creep

Real‑world projects often substitute drivers, CCT options, or lens kits while keeping the same “family name.” When reviewing the report:

• Match full model code – including any suffixes for CCT, lumen package, driver type, or optical option.
• Check driver description – dimmable vs non‑dimmable, 120–277 V vs 347–480 V, etc. Different drivers can shift spectrum slightly, especially under dimming.

If the LM‑79 lists a generic series name and not your exact catalog code, insist on either a revised report or a clear mapping statement from the manufacturer’s engineering team.

6.2 Component vs luminaire tests (LM‑79 vs LM‑80)

LM‑80 is often confused with LM‑79. The LM‑80‑21 overview clarifies that LM‑80 is a lumen maintenance test for LED packages, not for the finished luminaire; TM‑21 then uses LM‑80 data to project long‑term lumen and color maintenance.

For CRI verification, LM‑80 is not sufficient because:

• It usually tests LED packages at a few case temperatures in standardized fixtures, not with your luminaire’s optics and driver.
• Any color shift over time depends heavily on thermal design and drive current in the actual luminaire.

Actionable rule: Use LM‑79 for initial CRI and color metrics, and LM‑80/TM‑21 (or LM‑84) to judge whether those metrics will hold over 10,000–50,000 hours. This dual view is especially important for high‑CCT or high‑output fixtures that run hot and can drift green over time.

6.3 Hot vs room‑temperature performance

Most LM‑79 tests are run at 25 °C ambient. In high‑bay and industrial applications, actual ambient temperatures of 35–45 °C are common.

• Expect slightly lower lumens and modest CCT/CRI shifts at higher temperatures.
• When color is critical in a hot environment (e.g., metal casting inspection, food processing), ask vendors for elevated‑temperature LM‑79 data or real‑world photometric measurements.

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7. Step‑by‑Step: Using LM‑79 to Approve or Reject a CRI Claim

This section summarizes the process a seasoned specifier or facility manager can follow on any project.

7.1 Step 1 – Gather documents

Request from the vendor:

• Full LM‑79 PDF for the exact SKU and CCT.
• Any LM‑80 and TM‑21 (or LM‑84) documents for the LED source.
• If applicable, TM‑30 data or SPD file (CSV) for independent analysis.

7.2 Step 2 – Validate the report

Using the checklist from Section 2:

1. Confirm model number, CCT, and driver match the catalog and your submittal.
2. Verify that the lab is accredited and listed in a directory such as NVLAP.
3. Check that the test date is credible—ideally within 3 years for new runs or significant design revisions.
4. Confirm LM‑79 version, test method, and clear test conditions.
5. Find the uncertainty statement; note CRI and CCT uncertainties.

7.3 Step 3 – Compare catalog values to LM‑79

Create a quick comparison table for each candidate luminaire:

Field	Catalog Spec	LM‑79 Tested	Pass/Flag Rule
CCT	5000 K	4920 K	Pass if within 100–150 K.
CRI (Ra)	90	88.7	Pass if within ±2 points and R9 meets spec.
R9	50	47	Pass if within 5–10 points where high reds matter.
Lumens	20,000 lm	19,200 lm	Pass if within agreed tolerance (often ±10%).
Input Power	150 W	148 W	Confirm consistent for efficacy and code compliance.

Flag any metric that falls outside your acceptance rules and request clarification or alternate data.

7.4 Step 4 – Evaluate fitness for the specific application

For each space type, the “good enough” threshold changes:

• Warehouse / storage

  • Focus: lm/W, total lumen output, basic CRI ≥ 80.
  • LM‑79 priority: efficacy, delivered lumens, basic color acceptable.

• Manufacturing QA, assembly, or process inspection

  • Focus: accurate color discrimination of parts, labels, or finishes.
  • LM‑79 priority: CRI ≥ 90, R9 and other special indices high enough, plus stable CCT.
  • For deeper guidance, see focused discussions like specifying CRI 90+ in manufacturing plants or high‑CRI UFO high bays for quality control zones.

• Retail, showrooms, and branded spaces

  • Focus: saturation and “pop” as much as fidelity.
  • LM‑79 priority: strong Ra plus TM‑30 R_f/R_g values (where available) that support vivid but natural colors.

7.5 Step 5 – Document decisions and protect yourself contractually

For larger projects, it is worth formalizing your expectations:

• Include in specs:

  • “Manufacturer shall provide LM‑79‑19 test reports from an accredited lab for each luminaire type, matching specified CCT and driver options, including full R1–R15 data and spectral power distribution.”
  • “Manufacturer shall provide LM‑80 and TM‑21 data for primary LED sources.”

• In contracts or purchase orders, consider:

  • A sampling plan (e.g., random third‑party LM‑79 validation on delivered production units).
  • Remedies if delivered products materially underperform the LM‑79 data.

This approach aligns with good practice in public and institutional projects, where documentation and reproducibility are as important as the fixtures themselves.

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8. Expert Warning: When an LM‑79 Isn’t Enough

Even a high‑quality LM‑79 has limitations that matter in real projects.

1. Missing SPD or R1–R15 tables
   A surprising number of commercial “LM‑79” PDFs omit the SPD or full color index table, giving only Ra and CCT. As noted in real‑world analyses of sample LM‑79 documents such as this commercial downlight report, you cannot independently recalculate CRI or derive TM‑30 without the spectrum. Treat such documents as marketing summaries, not technical certificates.

2. No insight into long‑term color shift
   LM‑79 is a snapshot at a few hours of operation. To know if CRI and CCT hold up at 10,000–25,000 hours, you must read LM‑80/TM‑21 or LM‑84 data for lumen and color maintenance, as summarized in overviews like the LM‑79 vs LM‑80/TM‑21 guide.

3. No guarantee of installation equivalence
   If your site voltage, ambient temperature, or dimming regime differ greatly from test conditions, your actual color performance can diverge. This is especially true with high‑output industrial luminaires that run hot and spend a lot of time at partial dim levels.

Takeaway: use LM‑79 as your baseline for CRI verification, but layer on long‑term maintenance data and real‑world operating conditions when you are designing for color‑critical environments.

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9. Key Takeaways

• Do not trust the Ra in the brochure without an LM‑79. The only meaningful CRI verification comes from a complete luminaire LM‑79 report from an accredited lab.
• Check the report first, then the numbers. Confirm SKU match, lab accreditation, LM‑79 version, and test conditions before you compare CRI values.
• Account for measurement uncertainty. Differences of 1–2 points in Ra are normal; focus on bigger deviations and on R9 and the R1–R15 profile.
• Look beyond Ra. Healthy R9 and, where available, TM‑30 R_f/R_g are essential for spaces where color accuracy and visual appeal matter.
• Use LM‑80/TM‑21 alongside LM‑79 when you care about color stability over the life of the installation, not just day‑one performance.
• Document expectations in specs and contracts so everyone—from manufacturers to inspectors—understands what “CRI 90” is supposed to mean on your project.

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Frequently Asked Questions

How do I know if an LM‑79 report is real?

Check that it:

• Lists the exact model and CCT you are buying.
• Comes from a lab you can find in an accreditation directory such as NVLAP.
• States LM‑79‑19 or LM‑79‑08 as the test method, and includes test conditions, measurement uncertainty, and a clear color data table.
• Provides either the full R1–R15 indices or an SPD curve.

If any of these elements are missing, ask the vendor for a more complete report before you rely on it.

Can I verify CRI in the field with a handheld meter instead of LM‑79?

There are handheld spectrometers that estimate CRI, but they generally do not match the controlled conditions and uncertainty analysis of a proper LM‑79 test. For basic sanity checks they are useful, but for specifications, payback calculations, or disputes, CRI should be taken from a lab LM‑79 report.

Why do two different labs give slightly different CRI results for the same fixture?

Different labs use different instruments and calibration chains, so small differences are expected. LM‑79‑19 requires each lab to report measurement uncertainty, typically around ±1–2 CRI points for Ra. As long as both results fall within that combined uncertainty band, the difference is usually not operationally significant.

Is CRI 80 ever “good enough,” or should I always insist on 90+?

CRI 80 is perfectly serviceable for warehouses, back‑of‑house, and many industrial spaces where color discrimination is not critical. Reserve CRI 90+ and high R9 for areas where people evaluate products, faces, or finishes, such as retail, inspection lines, or healthcare. For more nuance in that trade‑off, see detailed analyses like the guide on when to specify CRI 90+ in manufacturing.

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Safety & Compliance Disclaimer
This article is for informational purposes only and does not constitute engineering, safety, or legal advice. Always consult the applicable IES, IEC, and local electrical and building codes, and work with qualified design professionals and accredited laboratories when specifying, installing, or verifying lighting equipment.

Sources

• ANSI/IES LM‑79‑19 – Optical and Electrical Measurements of Solid‑State Lighting Products
• CIE Method of Measuring and Specifying Colour Rendering of Light Sources
• Sample Commercial LM‑79 Report – RLUX Stella Shoebox
• IES TM‑30‑18 – IES Method for Evaluating Light Source Color Rendition
• Understanding LM‑79, LM‑80 and TM‑21 LED Tests
• NVLAP – Accredited Laboratories Directory
• PQL Lighting – Example LM‑79 Report