What Is an IES File?

This article describes what an IES file is, how to open one from your computer or online, and how to convert one to a different format that's compatible with other software programs.

What Is an IES File?

A file with the IES file extension is an IES Photometric file that stands for Illuminating Engineering Society. They are plain text files that contain data on light for architectural programs that can simulate light.

Lighting manufacturers might publish files in this format to describe how various structures are affected by their product. The program using the file can interpret it to understand how to display the correct lighting patterns on things like roads and buildings.

How to Open an IES File

There are several compatible programs: Photometrics Pros, Photometric Toolbox, Autodesk's Architecture and Revit software, RenderZone, the Visual lighting software, and Photopia.

Another way to open one for free is with IES Viewer or LITESTAR 4D Open, or online through Visual Photometric Tool.

A simple text editor, like Windows Notepad or one from our Best Free Text Editors list, can also open IES files because they're just plain text. Doing this won't let you see any visual representation of the data, though, just the text content.

How to Convert an IES File

An IES file can be converted to an EULUMDAT file (.LDT) using this online converter at appspot.com. You can also do the opposite—convert LDT to IES. Eulumdat Tools should be able to do the same thing, but it works from your desktop instead.

PhotoView isn't free but can convert one to formats like LDT, CIE, and LTL.

The free IES Viewer mentioned above can save the file to BMP.

Although it likely won't be of any use, you can save it to another text-based format using Notepad++.

The free DIALux program can open ULD files, which are Unified Luminaire Data files—a similar format to IES. You might be able to import an IES file into that program and then save it as a ULD file.

Still Can't Open It?

It's easy to mistake one file for another if their file extensions are similar. Since IES is three common letters, it's likely that if your file won't open with the suggestions above, it's because you're misreading that suffix.

For example, ISE files share the same letters, but they're either InstallShield Express Project files or Xilinx ISE Project files, meaning they open with different programs (InstallShield or ISE Design Suite).

An EIP file looks similar as well, but it, too, is actually completely different. If you have one of those files, it's probably an image created by Capture One.

Keep in mind that "i" is the first letter, not "L." So a file extension like LESS (used as a web page style sheet) is also different.

More Information on IES

The IES file format is called such because of the Illuminating Engineering Society. It's a society that brings together lighting experts (lighting designers, consultants, engineers, sales professionals, architects, researchers, lighting equipment manufacturers, etc.) to better design lighting conditions in the real world.

It's the IES that has ultimately influenced the creation of various standards for some lighting applications, like those used in healthcare facilities, sporting environments, offices, etc. Even the National Institute of Standards and Technology has referenced publications by the IES when it comes to Optical Radiation Calibrations.

Published by IES, The Lighting Handbook: 10th Edition is the authoritative reference for lighting science.