ies files

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 IES files to describe how various structures are affected by their product. The program using the IES file can interpret it to understand how to display the correct lighting patterns on things like roads and buildings.

How To Read Ies Files?

IES files can be opened with Lighting Analysts’ Photometric Toolbox, Autodesk’s Architecture and Revit software, RenderZone from AutoDesSys, AcuityBrands’ Visuallighting software, and LTI Optics Photopia.

An IES file can also be opened for free with IES Viewer, as well as online through AcuityBrands’ Visual Photometric Tool.

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

ISE files share the same letters as the .IES file extension. However, ISE files are either InstallShield Express Project files or Xilinx ISE Project files; they open with InstallShield and ISE Design Suite, respectively. The EIP file extension looks similar too but is instead image files created by Capture One.

If you find that an application on your PC does try to open the IES file but it’s the wrong application or if you would rather have another installed program open IES files, change the default program in Windows.

How To Convert An IES File

An IES file can be converted to an EULUMDAT file (.LDT) using this online converter. You can also do the opposite and convert LDT to IES. Eulumdat Tools should be able to do the same thing but it works from your desktop instead of through your web browser.

PhotoView isn’t free but can convert IES files to formats like LDT, CIE, and LTL.

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

Though it likely won’t be of any use, you can convert an IES file to another text-based format using the Notepad++ program mentioned above.

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.

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 (e.g. 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.

More Help With IES Files

See Get More Help for information about contacting me on social networks or via email, posting on tech support forums, and more. Let us know what kinds of problems you’re having with opening or using the IES file and we’ll see what we can do to help.

IES and LDT files for lighting design

Most of our LED lighting products have IES and/or LDT file available, to be used in lighting design programs such a RELUX and DIALUX.

Please look in the “Downloads” section on the product pages to download the files. For an example click here

Integral LED products are also listed on the RELUX program.

As explained above is the height of the luminaire housing not included in the IES file format. The manufacturer themself cannot enter the height in the IES format too. All information about the housing cannot be displayed. The IES file just describes the light emitting surface. This is a weak point of this format. 

But to support IES files in DIALux anyway we have implemented following behaviour. 

1. By default the height of the housing is 0,1m or as height as the light emitting surface. 

2. The user can override the default height with the correct height. The correct height can be e.g. looked up on the website of the manufacturer. 

DIALux Partner can benefit from the ULD format which improves some weaknesses of other photometric formats. So if possible we recommend to provide the ULD file instead of IES or LDT files for easier planing and more accurate results. We are wondering that they did not support the ULD file even they are DIALux Partner. 

Because always I had hard times with understanding and using IES files, I decided it’s time to put some light in it. And also, to share with you my findings.

Each field in the file must begin on a new line and must appear exactly in the following sequence:

  1. IESNA91
  2. [TEST] The test report number of your data
  3. [MANUFAC] The manufacturer of the luminaire
  5. 1
  6. The initial rated lumens for the lamp used in the test or -1 if absolute photometry is used and the intensity values do not depend on different lamp ratings.
  7. A multiplying factor for all the candela values in the file. This makes it possible to easily scale all the candela values in the file when the measuring device operates in unusual units—for example, when you obtain the photometric values from a catalog using a ruler on a goniometric diagram.
    Normally the multiplying factor is 1.
  8. The number of vertical angles in the photometric web.
  9. The number of horizontal angles in the photometric web.
  10. 1
  11. The type of unit used to measure the dimensions of the luminous opening. Use 1 for feet or 2 for meters.
  12. The width, length, and height of the luminous opening. It is normally given as 0 0 0.
  13. 1.0 1.0 0.0 (i have no idea what is this)
  14. The set of vertical angles, listed in increasing order. If the distribution lies completely in the bottom hemisphere, the first and last angles must be 0° and 90°, respectively. If the distribution lies completely in the top hemisphere, the first and last angles must be 90° and 180°, respectively. Otherwise, they must be 0° and 180°, respectively.
  15. The set of horizontal angles, listed in increasing order. The first angle must be 0°. The last angle determines the degree of lateral symmetry displayed by the intensity distribution. If it is 0°, the distribution is axially symmetric. If it is 90°, the distribution is symmetric in each quadrant. If it is 180°, the distribution is symmetric about a vertical plane. If it is greater than 180° and less than or equal to 360°, the distribution exhibits no lateral symmetries. All other values are invalid.
  16. The set of candela values. First, all the candela values corresponding to the first horizontal angle are listed, starting with the value corresponding to the smallest vertical angle and moving up the associated vertical plane. Then, the candela values corresponding to the vertical plane through the second horizontal angle are listed, and so on until the last horizontal angle. Each vertical slice of values must start on a new line. Long lines may be broken between values as needed by following the instructions given earlier.

difference between IES and LDT files for lighting design

IES Files are a Photometric file that shows the total Luminous flux and luminous intensity of a source of light. The IES file is the most common format in North America but is also widely used in Europe. IES photometric data files can be formatted two different ways either LTD or IES. There are some differences but many similarities between the IES and LDT formats. Firstly, the LDT format contains lines that specify the correlated colour temperature (CCT) and colour rendering index (CRI). 

The IES file does not contain this data. However, both IES and LDT files can be formatted as either absolute or relative files. When absolute photometric measurements are performed, the luminous intensity values are recorded and the total luminous flux value is calculated from these values. When relative photometric measurements are taken, the candela values of the luminaire are measured but the total luminous flux of the lamp is measured separately from the luminaire itself. In a relative measurement, the luminous intensity values are reported in candelas per kilo lumen.

 This allows for the measurement of the efficiency of the luminaire by comparing the bare lamp lumens to the lumens of theluminaire. The candela per kilo lumen value from the fitting should therefore be independent of the luminous flux of the lamp, as it is entirely dependent on the design of the luminaire itself. However, in the age of LED lighting there is one big disadvantage associated with the use of relative photometric data files. The thermal performance of an LED will be different depending on whether it is mounted in a luminaire or as a bare lamp, and the lumen output will therefore be very different. Relative photometry in this case can lead to misleading results as the calculated efficiency value will be incorrect.

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