What is a photometric report?
A photometric report is a laboratory-tested document that quantifies how a lighting fixture produces and distributes light. Generated per the IES LM-79 standard for LED products, it includes measured data on total light output, intensity distribution at every angle, electrical consumption, and color characteristics. It is the only objective way to verify a fixture's performance before committing to a layout.
The report comes in two forms. The PDF report is the human-readable document — typically 5–15 pages of summary data, polar plots, illuminance grids, and coefficient of utilization tables. The IES file .ies is the machine-readable companion, formatted per ANSI/IES LM-63, that lighting design software like AGi32, DIALux, or Revit imports to run illuminance simulations.
Both originate from the same test: a goniophotometer measures the fixture's candela intensity at thousands of angular positions, while an integrating sphere captures total luminous flux. The result is a complete fingerprint of how that specific luminaire emits light — not a marketing estimate, but measured, repeatable data.
The summary page: what to look at first
Every photometric report opens with a summary or cover page. It should take less than 60 seconds to determine whether the fixture is in the right ballpark for your project. Here are the key data points and what each one tells you:
| Data point | What it tells you |
|---|---|
| Total luminaire lumens | Measured output of the complete fixture — not raw LED chip lumens. This is the number for layout calculations. |
| Input wattage | Actual power draw at the wall, including driver losses. Use for energy code compliance and operating cost estimates. |
| Luminaire efficacy | Lumens ÷ watts. DLC Premium requires ≥ 120–135 lm/W depending on fixture category. |
| CCT (Kelvin) | Measured color appearance. Verify it matches the project spec (e.g., 4000K or 5000K). |
| CRI | Color accuracy vs. reference. Most commercial specs require ≥ 80; healthcare and retail often ≥ 90. |
| Rated life (L70 / L90) | Hours until lumen output degrades to 70% or 90% of initial. Typical LED target: L70 ≥ 50,000 hrs. |
| Test standard | Should cite IES LM-79 and LM-80 / TM-21. No standard referenced = question the data. |
| Test laboratory | Look for NVLAP-accredited or equivalent independent lab. Self-testing without oversight is a yellow flag. |
Lamp lumens vs. luminaire lumens — The report should state luminaire lumens, not lamp (source) lumens. Lamp lumens represent raw LED chip output before optical losses. Luminaire lumens reflect what actually exits the fixture. The difference can be 10–25%, and confusing the two leads to under-lit spaces.
How to read a candela distribution curve
The candela distribution curve — the circular, spider-web-looking chart — is the most information-dense graphic in any photometric report. It shows luminous intensity (in candelas) at every vertical angle, revealing the shape of the beam in a way no single number can.
What the axes represent
The radial axis represents candela values — farther from center means higher intensity at that angle. The angular axis shows vertical angles: 0° is straight down (nadir) and 90° is horizontal. Some outdoor reports extend past 90° to capture uplight and backlight.
Understanding the photometric planes
Most reports plot at least two planes: the 0° plane (along the fixture's length) and the 90° plane (across the width). When both lines overlap, the distribution is symmetric. When they diverge, the fixture has an asymmetric distribution — classified using IESNA Type designations (Type I through Type V), common in roadway, wall-pack, and area lighting applications.
Practical interpretation
- A tight, narrow peak at 0° = concentrated downlight beam. Typical of high-bay fixtures for 25–40 ft mounting heights in warehouses and manufacturing.
- A batwing pattern (lobes peaking at 30–40° with a dip at 0°) = wider, more uniform coverage at close spacing. Common in offices and retail.
- A forward-throw asymmetric pattern (intensity concentrated at 60–75° in one plane) = projection over distance. The profile of area lights, floodlights, and roadway luminaires.
Zonal lumen summary and light output ratios
The zonal lumen summary breaks the fixture's total output into angular zones — typically 0–30°, 0–60°, 0–90°, and 90–180°. While the candela curve shows beam shape, this table quantifies how much total light falls within each zone.
For a downlight or high-bay fixture, you want 90%+ of lumens in the 0–90° zone. Lumens above 90° is uplight — wasted energy in a warehouse, and a light-pollution contributor outdoors. A well-designed LED high bay typically delivers 95%+ below the horizontal plane.
BUG ratings for outdoor fixtures
For outdoor fixtures, zonal lumen data feeds directly into the BUG rating — Backlight, Uplight, and Glare (IES/IDA classification). Each component is rated 0–5 (lower is better). Many municipalities now specify maximum BUG values for light trespass and dark-sky compliance.
Reading foot-candle and illuminance grids
The illuminance grid shows predicted light levels across a surface for a single fixture at a specified mounting height. Each number represents foot-candles (fc) at that calculation point.
Mounting height multipliers
The grid is calculated at a reference mounting height. If yours differs, multiply each value by (reference height ÷ actual height)². A grid at 25 ft used for a 30 ft mount: each value × (25/30)² = × 0.69. A 20% increase in height means a 31% drop in illuminance.
Uniformity ratios
- Average-to-minimum (avg/min): Average illuminance ÷ lowest value. Most commercial interior codes target ≤ 3:1.
- Maximum-to-minimum (max/min): Highest ÷ lowest. If this exceeds 10:1, expect visible dark spots between fixtures.
Recommended foot-candle levels by application
| Application | IES recommended fc | Uniformity (avg/min) |
|---|---|---|
| Warehouse — general storage | 10–30 fc | 3:1 |
| Warehouse — order picking | 30–50 fc | 3:1 |
| Manufacturing — general | 30–50 fc | 3:1 |
| Office — open plan | 30–50 fc | 3:1 |
| Retail — general merch. | 50–100 fc | 3:1 |
| Parking lot — open | 1–5 fc | 4:1 IES RP-8 |
| Parking garage | 5–10 fc | 4:1 |
| Roadway — local | 0.6–1.2 fc avg | 6:1 IES RP-8 |
| Healthcare — corridor | 10–20 fc | 3:1 |
| Healthcare — exam room | 50–75 fc | 3:1 |
Reference: IES Lighting Handbook, 10th Edition; IES RP-8-18. Confirm applicable edition and local amendments for your jurisdiction.
Coefficient of utilization tables
Coefficient of utilization (CU) tables appear primarily in indoor area lighting reports. They answer a direct question: what percentage of the fixture's total lumens will reach the work plane in a given room?
How to read the table
CU tables show Room Cavity Ratio (RCR) on one axis and ceiling/wall reflectance on the other. RCR captures room proportions relative to mounting height:
H = cavity height (fixture to work plane) · L = length · W = width
Low RCR (1–2) = large room, light reaches the work plane efficiently. High RCR (8–10) = small or tall room where walls absorb more light.
Using CU for fixture quantity
LLF (Light Loss Factor) = typically 0.85–0.90 for clean LED installations
CU values are specific to each fixture — different optics produce different CU values even at identical lumen output. Outdoor reports generally don't include CU tables.
IES files — the data behind the report
The IES file .ies is the machine-readable companion to the PDF. Formatted per ANSI/IES LM-63, it feeds into AGi32, DIALux, Revit, and Visual for project-specific simulations.
What's inside an IES file
Open any .ies in a text editor and you'll see:
Red flags in IES files
Missing test lab reference — data may be estimated, not measured.
Wattage mismatch — IES watts must match spec sheet for the quoted configuration.
Suspiciously high efficacy — 200+ lm/W for standard commercial? Something is off. Mainstream range: 100–160 lm/W.
No date — could represent an older, discontinued product revision.
Always request the IES file for the exact catalog number, wattage, optic, and CCT being specified. If a manufacturer can't provide one, that's a serious red flag. Jarvis Lighting publishes IES files for every product configuration — available on each product page or by request.
Comparing fixtures using photometric data
The real value of understanding photometric reports comes when you use the data to compare fixtures for the same project. The goal: apples-to-apples — same mounting height, same room conditions, same calculation methodology.
What to prioritize by application
Efficiency + Uniformity
Prioritize lm/W for energy savings and rebate qualification. Check uniformity ratio. Verify minimal uplight via zonal lumens.
BUG Rating + Distribution
Prioritize BUG rating for code compliance. Match distribution type (III/IV for perimeter, V for center). Check uniformity per IES RP-8.
Glare + Color Quality
Prioritize CRI ≥ 80 (≥ 90 healthcare). Target UGR ≤ 19 for offices. Match CU values to room geometry.
Photometrics and rebates — DLC listing requires independent LM-79 test data meeting specific efficacy thresholds. Verify both fixtures are DLC-listed for the exact configuration being quoted — a fixture may be listed at one wattage but not another.
Common mistakes when reading photometric reports
Even experienced professionals make these errors. Catching them before they affect a layout saves time, money, and rework.
Confusing lamp lumens with luminaire lumens. LED chip output is always higher than fixture output after optical/thermal losses. If the spec sheet says 20,000 lm but the report says 17,200 lm — the report shows the correct number.
Ignoring light loss factors. Photometric data = initial output. Apply LLF (typically 0.85–0.90 clean, 0.70–0.80 industrial) — a layout at initial values will underperform within 2–3 years.
Using IES data from the wrong configuration. A fixture in 100W/150W/200W versions has three different IES files. Distribution shape may change at different drive currents — not just scale.
Trusting a layout without checking assumptions. Verify mounting height, tilt, spacing, reflectances, and maintenance factor. Best-case assumptions produce best-case numbers.
Not verifying IES file matches the quoted fixture. On multi-product submittals, files from different models or older revisions can be included by mistake.
Accepting heat maps without checking numerical uniformity. A sea of green tells you nothing if the legend ranges from 1 fc to 100 fc. Always check avg/min and max/min ratios.
Frequently asked questions
What is the difference between a photometric report and a photometric plan?
A photometric report is laboratory test data for a single lighting fixture — measured intensity distribution, lumen output, and electrical characteristics, per IES LM-79. A photometric plan (or lighting layout) is a computer simulation that models how one or more fixtures will illuminate a specific space, using IES files as inputs. The report tells you how the fixture performs; the plan tells you how your space will perform.
What does LM-79 mean on a photometric report?
IES LM-79 is the approved testing method for LED lighting products. It standardizes measurement of total luminous flux, luminaire efficacy, intensity distribution, CCT, and CRI in a controlled lab setting. An LM-79 reference means the fixture was tested under this recognized standard — a prerequisite for DLC listing and most utility rebate programs.
How do I get IES files for lighting fixtures?
Most reputable manufacturers publish IES files on their website — on product pages or in a downloads section. If you can't find it, contact the manufacturer for the specific catalog number, wattage, optic, and CCT. If they cannot provide an IES file, treat that as a significant red flag regarding data transparency.
What is a good uniformity ratio for commercial lighting?
For general commercial interiors, IES recommendations target avg/min of 3:1 or better. For open parking lots, IES RP-8-18 recommends 4:1. For roadways, typically 6:1 depending on classification. Lower ratios (closer to 1:1) mean more consistent illumination.
Can I read a photometric report without lighting design software?
Yes. The PDF report is designed to be readable without specialized software — summary page, candela curves, zonal lumen tables, illuminance grids, and CU tables are all in human-readable format. Software (AGi32, DIALux) is only needed to import the IES file and run project-specific simulations.
How often should photometric data be updated?
Whenever the fixture design changes — LED module, driver, optic, reflector, lens, or housing modifications all affect the data. A fixture tested in 2019 that received an LED upgrade in 2023 should have a new report. Check the test date and confirm it represents the current production version.
