How to Read an LM-79 Report for LED High Bays

Demystifying an LM-79 report is one of the fastest ways to separate a spec-grade UFO high bay from a commodity fixture. LM-79 is not a logo or a pass/fail stamp; it is a standardized snapshot of optical and electrical performance. If you can read that snapshot, you can verify lumen output, efficacy, color quality, and whether the IES file you are using in your warehouse layout is trustworthy.

This guide walks contractors, facility managers, and specifiers through LM-79 reports with a focus on LED high bays, using the structure of the standard from the Illuminating Engineering Society (IES) and field-proven review habits.

Diagram-like scene showing how an LM-79 report connects lumens, watts, and light distribution for a warehouse high bay layout

1. LM-79 in Context: What It Is (and Isn’t)

1.1 Purpose of LM-79 for LED High Bays

ANSI/IES LM-79-19 is the approved method for measuring the total luminous flux, electrical power, efficacy, color characteristics, and distribution of solid-state lighting products, including complete UFO high bay luminaires. According to Intertek’s overview of LM-79 testing, the method specifies how to measure lumens, watts, efficacy (lm/W), correlated color temperature (CCT), color rendering index (CRI), and power factor under controlled conditions.

For high bays, LM-79 is the basis for:

DLC (DesignLights Consortium) QPL qualification, which in turn governs most utility rebates via the DLC Qualified Products List.
Meeting minimum efficacy thresholds in energy codes like ASHRAE 90.1 and the IECC.
Providing accurate photometric files (.ies, LM‑63 format) for tools such as AGi32.

1.2 LM-79 vs. LM-80/TM-21 and Safety Listings

A common misconception is that “it has an LM-79” means a luminaire is high quality. LM-79 alone does not address long-term lumen maintenance or safety.

LM-79: Measures integrated fixture performance at a given point in time.
LM-80-21: Measures LED package or module lumen maintenance over thousands of hours, as defined by the IES LM-80 standard.
TM-21-21: Uses LM-80 data to project long-term L70/L90 life per IES TM-21-21.
UL/ETL listings: Verify that the luminaire meets safety standards such as UL 1598 (luminaires) and UL 8750 (LED equipment), or equivalent.

LM-79 is therefore one piece of a compliance stack, not a stand‑alone quality seal. Experienced specifiers always request LM-79 alongside LM-80/TM‑21 and safety listings when evaluating high bays for long‑cycle industrial projects.

1.3 Test Conditions: The “Snapshot” Problem

LM-79 tests are typically performed at 25 °C ambient with the luminaire in thermal equilibrium. As highlighted by Intertek’s LM-79 guidance, this provides a consistent baseline but does not represent hot ceilings in real warehouses.

Field measurements show that when the case temperature (Tc) of a high bay rises from 25 °C to 40–50 °C, lumens and efficacy often drop by 5–20%, depending on driver efficiency and heat sinking. In practice, this means:

LM-79 lumens are initial values under ideal lab conditions.
Designers usually apply maintenance factors (often 0.70–0.85 over 5 years for dusty or poorly ventilated warehouses) to estimate end-of-life illuminance.

Implication for you: never treat LM-79 lumen and efficacy values as the guaranteed light level on the floor after years of operation. They are your starting point, not your finish line.

2. How an LM-79 Report Is Structured

Most accredited labs follow a similar structure. Understanding where to look saves time and avoids errors.

2.1 Cover Page and Accreditation Details

The first items to verify:

Lab accreditation: Confirm an NVLAP or IAS-accredited lab name and accreditation number.
Report number and date: Many specifiers prefer reports issued within the last 3–5 years, or a statement that the test reflects the current LED boards and drivers.
Luminaire identification: Catalog number, description (e.g., “UFO LED high bay, 150 W, 5000 K”), any accessory optics or lenses attached.
Orientation and mounting: Pendant vs hook vs surface; downlight or uplight; enclosure orientation.

Expert habit: Experienced reviewers always cross-check that the catalog number, description, and configuration match what is being specified or purchased. Silent driver or LED board changes can invalidate older reports.

2.2 Test Conditions and Stabilization

The “Test Conditions” section describes:

Ambient temperature (Ta): Often 25 °C ± 1 °C.
Supply voltage and frequency: For high bays, 120–277 V, 50/60 Hz or similar.
Stabilization method: LM-79 requires that the luminaire reach thermal equilibrium before readings are taken.

This section tells you how comparable different reports are. If one product is tested at a lower ambient or with a different driver setting, you should be cautious when comparing efficacy.

2.3 Electrical and Photometric Summary

The “Summary” or “Results” table typically includes:

Input power (W)
Input current (A)
Power factor (PF)
Total harmonic distortion (THD), if provided
Total luminous flux (lumens)
Efficacy (lm/W)
CCT and Duv
CRI (Ra) and sometimes R9

This is the section most buyers focus on, but reading it in isolation is a mistake. To correctly interpret these values, you need the details in the following sections.

3. Reading the Key Numbers for High Bay Specification

3.1 Lumens and Efficacy: Beyond “Higher Is Better”

LM-79 total lumens and efficacy tell you how efficiently the fixture converts watts into light, but for high bays the distribution of that light matters as much as the quantity.

A frequent myth is that the highest-lumen high bay always delivers the brightest work plane. In reality, as practitioners know and as reflected in IES design guides like ANSI/IES RP‑7, a lower‑lumen fixture with a tighter beam can deliver higher illuminance on the task area than a higher‑lumen fixture with a very wide beam.

Practical example:

Fixture A: 30,000 lm, 90° beam, 150 W → 200 lm/W.
Fixture B: 24,000 lm, 60° beam, 150 W → 160 lm/W.

At a 35 ft mounting height, Fixture B can deliver 15–25% higher average foot‑candles on the floor in a narrow-aisle warehouse, because more of its light is directed downward where it is needed.

When reading an LM-79 report:

Use efficacy to screen products: DOE’s FEMP performance specification for high-efficiency luminaires shows typical lm/W ranges for commercial/industrial luminaires and sets minimum thresholds for energy-efficient purchasing.
Use lumens + distribution (candela tables or IES file) to determine spacing and mounting height.

For more on tying lumens to actual layout decisions, see the dedicated guide on warehouse lumens for UFO high bays.

3.2 CCT and Color Consistency

LM-79 reports list CCT (e.g., 4000 K or 5000 K) and chromaticity coordinates. To ensure consistency across projects and manufacturers, ANSI C78.377 defines standardized chromaticity quadrangles for common CCTs such as 3000 K, 3500 K, 4000 K, and 5000 K. The ANSI C78.377-2017 standard specifies that products labeled with a given CCT must fall within these tolerance regions.

What to check:

Target CCT vs measured CCT: Is a “5000 K” product actually close to 5000 K, or does the report show 4700 K or 5300 K?
Duv: Values close to zero appear neutral; large positive or negative deviations can make light look noticeably greenish or pinkish.

For facilities where visual comfort and color preference matter (e.g., mechanics’ bays, inspection areas), matching CCT across all luminaires is critical. If you are deciding between 4000 K and 5000 K, the community discussion summarized in resources such as the Garage Journal threads aligns well with ANSI’s tolerance bands; 4000 K tends to feel warmer and less harsh, while 5000 K supports higher contrast. A detailed comparison is explored in many color temperature guides for garages and workshops.

3.3 CRI and R9: When Color Really Matters

LM-79 reports typically provide CRI (Ra). Some labs also provide extended metrics like R9 (saturated red). For general warehouse storage, a CRI of 70–80 is often adequate. For tasks involving color discrimination—such as product inspection, mechanical work, or photography—designers often specify CRI ≥ 80 and positive R9.

A powerful but underused step is to request the spectral power distribution (SPD) and R9 values for critical applications. As noted in the practitioner insights, many buyers simply check Ra, but SPD and R9 are what determine whether reds and skin tones look natural in real use.

3.4 Power Factor and THD: Grid-Friendly High Bays

Energy standards such as ASHRAE 90.1 and common utility rebate programs typically require high power factor (≥ 0.9) and controlled total harmonic distortion (THD). LM-79 reports often provide:

Power factor: Closer to 1.0 is better; values above 0.9 are considered “high power factor” and reduce wasted reactive power.
THD: Lower THD means the driver injects fewer harmonics into the electrical system, which is beneficial in facilities with sensitive equipment.

One of the research insights emphasizes that buyers sometimes equate input watts in LM‑79 with driver quality, while a separate driver efficiency line (if given) is more informative. Two luminaires with identical lumens and watts can differ in driver efficiency, leading to different internal temperatures and therefore different long‑term lumen maintenance.

4. Photometric Distribution: Using LM-79 Like a Lighting Designer

4.1 IES Files and LM-63 Data

LM-79 reports for high bays usually include either:

An embedded photometric table (cd values at various vertical and horizontal angles), or
A reference to an external .ies file generated according to the IES LM-63-19 standard.

These files are what lighting software such as AGi32 uses to calculate illuminance, uniformity, and glare. Without an accurate IES file, it is impossible to create reliable layouts for warehouses, gyms, or production floors.

Expert habit: Always verify that the IES file name, revision date, and luminaire catalog number referenced in the LM‑79 report match the product used in your design. One of the research insights stresses that using an old IES file—even if lumens match—can leave you designing around an outdated optic or driver.

4.2 Candela Tables and Beam Character

LM-79 candela tables look intimidating at first, but a few simple checks go a long way:

Peak candela and distribution: High peaks at low angles suggest a narrow beam; broader peaks spread over mid-angles suggest a wide beam.
Symmetry: For symmetric UFO high bays, horizontal planes should look similar; large differences can signal asymmetric optics.
Upward light: For some applications, uplight is desirable to brighten ceilings; in others (e.g., tall racking) it is wasted.

Research insight IG6 highlights that these distributions are not only for designers: they directly influence glare and uniformity. Under low ceilings (e.g., 12–16 ft shops), a very peaky distribution that works well at 30 ft can cause discomfort and bright spots.

For a deeper dive into balancing uniformity and glare in high bay optics, see the guide on low-UGR high bay lighting.

4.3 Spacing Criteria and Layout Implications

Many LM-79 reports or associated IES summaries provide spacing criteria (SC) values. SC gives a quick approximation of the maximum spacing between luminaires (in multiples of mounting height) while maintaining acceptable uniformity.

Example:

Mounting height: 30 ft
SC (along aisles): 1.2
Recommended spacing: 1.2 × 30 = 36 ft max along the aisle

In practice, designers often tighten this slightly to improve uniformity and to offset lumen depreciation over time. For step‑by‑step layout logic, the article on designing a high bay layout for warehouse safety provides a practical framework.

5. Pro Tip: Avoiding Common LM-79 Misreads

This section pulls together field-tested habits that prevent costly mistakes.

5.1 Expert Warning: Don’t Treat LM-79 as a Certification

The first research insight underscores a major pitfall: LM‑79 is often treated as a “certification,” but in reality it is simply a standardized test method and report. As Intertek’s LM-79 explainer makes clear, LM‑79 does not imply that a product has passed any minimum threshold; it only documents measured performance under prescribed conditions.

What this means for you:

Always pair LM-79 with LM-80/TM‑21 data, UL/ETL safety listings, and DLC QPL entries for a complete picture.
For rebate-driven projects, verify that LM-79 data supports the DLC category and version required by the utility’s program rules, then confirm eligibility via the DLC QPL.

5.2 Check Orientation, Optics, and Accessories

Another research insight points out that many specifiers skim past the sample orientation and configuration in the LM‑79 report. This is risky because:

A test performed without the standard lens, diffuser, or reflector will overstate lumens compared with the production configuration.
Uplight vs downlight mounting changes both lumens and thermal behavior.
Remote vs integral driver configurations can affect operating temperature and measured efficacy.

Checklist: Configuration sanity check

Use this quick checklist whenever you review an LM‑79 for a high bay:

Confirm the catalog number exactly matches your submittal.
Verify CCT and CRI match your spec (e.g., 4000 K, 80 CRI).
Confirm lens type (clear, frosted, prismatic) is the same as your intended option.
Check mounting method and orientation listed in the report.
Confirm driver configuration (integral vs remote, dimmable vs non-dimmable).
Verify IES file reference matches the catalog number and revision.

5.3 Efficacy vs Thermal Reality

Another research insight notes that many buyers assume LM-79 efficacy numbers reflect real operating conditions. In practice, high bays installed near hot ceilings can experience case temperatures 15–25 °C higher than the lab setup, cutting lumens and efficacy by 5–20%.

Experienced designers respond by:

Derating lumens in layouts using a combined maintenance factor that includes lamp lumen maintenance, luminaire dirt depreciation, and room surface depreciation. One research insight notes that designers often reduce LM-79 lumens by 20–30% to estimate end-of-life performance.
Preferring luminaires with robust thermal paths and high‑efficiency drivers, which run cooler and maintain light output better over time.

6. Turning LM-79 Data into Design Decisions

6.1 Quick Comparison Framework

Use the following table as a workhorse framework when comparing LM‑79 reports for different high bays in the same project.

Decision Question	LM-79 Fields to Check	What “Good” Looks Like (Typical, Not a Code Limit)	When to Be Cautious
Is it energy efficient enough for code/rebates?	Lumens, Watts, Efficacy, PF	Efficacy aligned with or above DOE FEMP high-bay ranges; PF ≥ 0.9	Efficacy significantly below peers; PF < 0.9, especially for large projects
Will it meet target illuminance?	Lumens + Candela/IES + SC	Lumens adequate and distribution matches mounting height and aisle geometry	Very high lumens with very wide beam at tall heights (wasted light) or narrow beam at low ceilings (glare)
Is the color suitable for tasks?	CCT, Duv, CRI, R9 (if available)	CCT consistent with project spec (e.g., 4000 K or 5000 K), CRI ≥ 80 for color-critical tasks	CCT far from nominal, low CRI or negative R9 where inspection or branding visuals matter
Will it play nicely with the electrical system?	PF, THD, Input current	High PF, moderate THD, current below circuit limits	High THD in facilities with sensitive electronics; marginal circuit loading
Is the data trustworthy and current?	Lab accreditation, date, catalog number, IES reference	NVLAP/IAS lab, report < 3–5 years old, catalog and IES file match product	No accreditation, very old report, mismatched catalog numbers or IES files

This framework reflects how experienced project reviewers triage candidate luminaires before running detailed layouts.

6.2 Case Study: Two 150 W High Bays for a 30 ft Warehouse

Consider a simple warehouse with 30 ft mounting height and typical open-floor racking. Two LM‑79 reports show the following:

High Bay 1:
- 22,000 lm, 150 W, 147 lm/W, 90° beam, PF 0.95.
- 5000 K, CRI 80, report dated last year.
High Bay 2:
- 24,000 lm, 150 W, 160 lm/W, 60° beam, PF 0.92.
- 5000 K, CRI 80, report dated five years ago.

Layout analysis in AGi32 with the corresponding IES files shows:

High Bay 1 delivers ≈ 28 fc average with very smooth uniformity across the floor.
High Bay 2 delivers ≈ 33 fc average but with pronounced bright bands and darker gaps, especially between aisles.

An experienced designer may choose High Bay 1 despite its lower lumens and efficacy on paper, because its beam shape and more recent LM‑79/IES data produce a safer, more uniform environment. This mirrors one of the research insights (IG2): higher lumens do not automatically equal better delivered performance.

For projects where worker safety and clear visibility are critical, pairing LM‑79 interpretation with uniformity-focused resources like the article on designing high bay layouts for warehouse safety is a prudent approach.

6.3 Connecting LM-79 to Controls and Codes

LM‑79 reports are also used to document base performance before adding controls. Energy codes such as ASHRAE 90.1, the IECC, and California Title 24 lighting standards require:

High-efficacy luminaires that support lower lighting power densities.
Mandatory controls (occupancy sensors, daylight response, multi-level dimming) in many warehouse and industrial spaces.

LM‑79 data provides the “full-output” reference point. When combined with control strategies documented by resources such as DOE’s wireless occupancy sensor applications guide, designers can quantify savings from stepped or continuous dimming.

For guidance on zoning high-bay dimming to meet both code and usability requirements, see the article on zoning UFO high bay dimming controls.

7. Step-by-Step LM-79 Review Workflow for High Bays

This workflow condenses the earlier sections into an actionable process for contractors, facility managers, and specifiers.

Verify the report and product identity
- Confirm NVLAP/IAS accreditation.
- Check report date (aim for within 3–5 years) and that the catalog number, CCT, and options match your submittal.
Scan the electrical and photometric summary
- Note watts, lumens, efficacy, PF, THD, CCT, and CRI.
- Compare efficacy to DOE FEMP or project baseline expectations.
Check configuration details
- Confirm mounting, orientation, lens type, and driver configuration.
- Ensure any accessories (guards, reflectors) match the field design.
Review distribution and IES file alignment
- Examine candela tables or import the provided IES (.ies, LM‑63) into AGi32 or similar.
- Confirm distribution suits mounting height and layout (open vs aisle, low vs high ceilings).
Confirm color quality for the application
- Ensure CCT aligns with the space’s needs (e.g., 4000 K for general warehousing, 5000 K for detailed tasks).
- Check CRI and R9 where color-critical tasks are performed.
Assess long-term performance context
- Pair LM‑79 lumen data with LM‑80/TM‑21 for L70 or L90 life estimates.
- Apply a realistic maintenance factor (e.g., 0.70–0.85 over 5 years) in layouts.
Document for code and rebates
- Use LM‑79 efficacy and wattage values in energy code compliance forms.
- Cross‑reference with DLC QPL entries and utility rebate forms.

Following this workflow standardizes how your team reviews high bay submittals and reduces the risk of performance surprises after installation.

8. Wrapping Up: LM-79 as Your High-Bay Truth Serum

When used correctly, an LM‑79 report is the closest thing you have to a truth serum for LED high bays. It tells you how the luminaire behaves under controlled conditions, exposes whether marketing lumens align with independently measured lumens, and anchors the IES files you rely on for layouts.

The key is to treat LM‑79 as part of a system:

Combine it with LM‑80/TM‑21 to understand long-term lumen maintenance.
Cross‑check it with UL/ETL listings and DLC QPL entries to validate safety and rebate eligibility.
Translate its photometric data into real‑world layouts using tools like AGi32, ASHRAE/IECC code requirements, and practical guides on lumens, uniformity, and controls.

For teams that regularly specify UFO high bays, building an internal LM‑79 review checklist and training installers and project managers on these fundamentals pays off in fewer callbacks, smoother inspections, and more predictable lighting performance over the full life of the system.

Frequently Asked Questions

What is LM-79 in simple terms?

LM‑79 is an IES-approved test method and report format that measures how a complete LED luminaire—such as a UFO high bay—performs in terms of lumens, watts, efficacy, color, and light distribution under controlled lab conditions. It is not a certification; it is a standardized performance snapshot.

Does an LM-79 report prove that a high bay is DLC listed?

No. LM‑79 provides the performance data (lumens, efficacy, color, etc.) that DLC uses to evaluate products, but DLC listing is a separate process. To confirm rebate eligibility, you must locate the exact catalog number on the DLC Qualified Products List.

How recent should an LM-79 report be?

Many specifiers prefer reports that are less than 3–5 years old or accompanied by a statement that the LED modules and drivers have not changed since testing. Older reports can hide silent component changes that alter performance.

Are LM-79 lumens the same as “delivered” lumens on the floor?

Not exactly. LM‑79 lumens are measured at the luminaire in a lab, typically at 25 °C. Designers apply maintenance factors to account for lumen depreciation, dirt, and real operating temperatures. Research and field practice show that designers often assume a 20–30% reduction between initial LM‑79 lumens and late‑life delivered light in high‑bay applications.

Does LM-79 include flicker and dimming behavior?

LM‑79 focuses on steady-state electrical and photometric performance. While some reports may mention dimming tests, LM‑79 does not fully characterize flicker or the shape of the dimming curve, especially under 0–10 V controls. For critical spaces, you should request dimmer/driver compatibility data and, where necessary, perform on-site mockups.

Safety and Compliance Disclaimer:

This article is for informational and educational purposes only. It does not constitute engineering, safety, legal, or compliance advice. Always consult a licensed professional engineer, qualified electrician, and the applicable standards and local codes (including but not limited to IES, UL/ETL standards, ASHRAE 90.1, IECC, Title 24, and the National Electrical Code) before selecting, installing, or modifying any lighting equipment or controls.

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How to Read an LM-79 Report for LED High Bays