Key Takeaways
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An IES file is a plain-text file built to the IES LM-63 standard that stores measured candela values for a specific fixture configuration, allowing lighting software to simulate how that fixture distributes light.
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The photometric distribution data used to create an IES file is generated through goniophotometer testing, which measures light intensity at different angles around a fixture. An integrating sphere serves a different purpose, measuring total lumen output and color data rather than generating the IES file.
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Importing an IES file into DIALux, AGI32, Revit, or AutoCAD lets you check footcandle levels and uniformity before a fixture is installed, helping avoid costly change orders.
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Matching an IES file to the exact part number, lumen package, and optics of a fixture matters more than matching the fixture type in general.
Before you install a fixture, you want to know where the light will actually land. That's exactly what an IES file helps you do. It gives lighting software the real photometric data for one specific fixture so you can see how it'll perform before it ever goes up.
Two fixtures can share the same wattage and lumen output and still light a room completely differently depending on how that light is distributed. An IES file is what lets you see that difference before you buy anything.
Contractors, facility managers, and lighting designers use IES files to check footcandle levels, plan fixture spacing, and avoid dark spots or glare before installation day. Homeowners rarely need to open the file directly, but understanding what the file does makes it easier to trust the specs for an LED fixture. e-conolight builds its product line around fixtures with reliable photometric data, which is exactly what an IES file provides.
What Is an IES File?
IES stands for the Illuminating Engineering Society. An IES file follows the LM-63 format for reporting photometric data and stores candela values that describe light intensity at different angles around a fixture.
Think of it as a lighting fingerprint. No two fixtures light a space the exact same way, so no two IES files look identical either, even when the products seem similar on paper.
A few things worth knowing about how these files work:
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Each IES file is tied to one exact fixture configuration, not a general category like "high bay" or "wall pack."
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The file includes the fixture's light distribution pattern, not just its total lumen output.
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Lighting design software reads the file and uses it to simulate how that fixture will actually perform in a real space.
An IES file does not tell you how bright a fixture looks in a catalog photo. It tells you how that fixture behaves once it is mounted, aimed, and turned on.
Architects, electrical contractors, and lighting designers rely on this data daily, but you do not need a lighting degree to understand the basics. Once you know what the file represents, the rest of the IES file format makes a lot more sense.
Inside the IES File Format
An IES file is a plain-text file, which might surprise people expecting something more complex. It follows the structure defined by the IES LM-63 standard, which allows the file to work consistently across different design programs.
A typical IES file is broken into a few sections:
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Section |
What It Contains |
|---|---|
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Header info |
Fixture identification, manufacturer, and test details |
|
Keywords |
Metadata such as lamp type, test lab, and issue date |
|
Photometric data |
Candela values by angle, lumen output, and tilt information |
The candela values used to create an IES file come from goniophotometer testing. A goniophotometer measures light intensity at different angles around a fixture, providing the distribution data recorded in the IES file.
An integrating sphere serves a different purpose. It measures total lumen output and color data, but it does not generate the angular distribution data used to create an IES file.
IES LM-79 uses absolute photometry for LED lighting products, but not every IES file is generated from LM-79 testing. IES files may contain absolute or relative photometric data depending on how the product was tested.
IES is not the only photometric format in use. LDT files serve a similar purpose and are more common in parts of Europe, but IES remains the standard most widely supported by US lighting design software. That is one reason the IES file format has stuck around for decades without much need to change.
How to Use IES Files in Lighting Design Software
Learning how to use an IES file does not require an engineering background, just an understanding of what the simulation output means for your specific space.
A general workflow looks like this:
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Import the IES file into your lighting design software, such as DIALux, AGI32, Revit, or AutoCAD.
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Place the fixture in your 3D model or floor plan at the intended mounting height and location.
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Aim the fixture, if adjustable, to match how it would actually be installed.
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Run an illuminance calculation to see projected footcandle levels across the space.
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Review uniformity across the layout, not just the average light level, since uneven lighting can be a bigger problem than low lighting.
This step matters more than it might seem. Catching a coverage gap in a simulation costs a few minutes. Catching it after fixtures are already installed can mean a change order, extra labor, and a delayed project. If you want to test fixture spacing and mounting height before committing to a layout, the e-conolight Lighting Layout Tool can help you map out coverage for a space using the specs of the fixtures you are considering.
Accurate manufacturer data makes all the difference here. If the IES file does not reflect the actual fixture, the simulation will not either, no matter how good the software is.
Why IES Files Matter When You Choose LED Fixtures
Specs on a product page tell part of the story. Lumens, wattage, and CCT matter, but they do not tell you where the light actually lands. Photometric data from an IES file fills that gap, showing how a fixture's light behaves in a real space rather than just how much light it produces on paper.
Two fixtures rated at the same lumen output can produce very different results depending on the distribution type. A wide, symmetric distribution spreads light evenly across an open area, like a parking lot. A narrow, asymmetric distribution throws light in a specific direction, which works better for lighting a wall or a building perimeter.
Here is how that plays out across common applications:
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Application |
Distribution Priority |
Fixture Type to Consider |
|---|---|---|
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Parking lots and large outdoor areas |
Wide, even coverage |
LED parking lot lights |
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Building exteriors and perimeters |
Directional throw along a wall |
LED wall pack lights |
|
Warehouses and industrial spaces |
High mounting height, downward focus |
LED high bay lights |
The candela distribution data stored in an IES file shows how a fixture directs light at different angles. Lighting design software can combine that data with variables such as mounting height, fixture location, and aiming to calculate projected light levels and uniformity across a space. Reviewing that data before purchasing can help you avoid buying a fixture that technically meets code but leaves dark corners or uneven coverage across a space. Results vary by fixture, mounting height, and space layout, so a simulation based on accurate photometric data is generally more reliable than lumen output alone.
Where to Find and Download IES Files for LED Fixtures
Manufacturers that publish reliable photometric data typically make it possible to download an IES file alongside a fixture's other specifications, though availability can vary by product. The most important step is matching the file to the exact part number, lumen package, and optics configuration you plan to purchase, since even small variations in a product line can change the distribution data.
A few tips for staying organized once you have the right file:
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Keep IES files organized by project, room, or fixture type rather than in one large folder.
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Double-check the file name against the fixture's part number before importing it into design software.
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If a fixture has multiple lumens or optic options, confirm which version the IES file represents before running a simulation.
If you cannot locate the IES file you need for an e-conolight fixture, reaching out directly is often the fastest path to accurate data.
Common IES File Questions and Troubleshooting Tips
Most IES file issues come down to a handful of common causes, and most have a quick fix.
File will not import. Check that the file has a valid .ies extension and was not corrupted during download. Some older software versions also have trouble with newer LM-63 revisions.
Simulation looks too bright or too dim. Verify the mounting height and units (feet versus meters) entered into your design software. A mismatch here throws off calculations even when the IES file itself is accurate.
Results do not match expectations. This is often a sign that the wrong IES file was used, such as one meant for a different lumen package or optic than the fixture actually being installed. Confirming the part number against the file name usually resolves it.
If none of these steps solve the issue, or if you are unsure whether you have the correct file for a specific e-conolight fixture, contact us to help track down the right data for your project.
FAQ
What is an IES file used for?
An IES file is used by lighting design software to simulate how a specific fixture distributes light in a real space, helping plan footcandle levels, spacing, and uniformity before installation.
Is an IES file the same as an LDT file?
No. Both formats store photometric data, but IES follows the LM-63 standard and is more commonly used in the US, while LDT is more common in parts of Europe.
Do I need special software to open an IES file?
Yes. IES files are read by lighting design and simulation programs such as DIALux, AGI32, Revit, or AutoCAD rather than standard text or document editors.
Can I use an IES file for a fixture different from the one it was tested on?
This is not recommended. Because each IES file reflects one specific fixture configuration, using it for a different product can produce inaccurate simulation results.
