Free online LDT to IES converter
Convert EULUMDAT LDT photometric data to an LM-63 IES file and verify orientation and flux.
Convert LDT to IES online - free
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How to convert ldt to ies file
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Lighting-design, CAD, BIM, and rendering software may accept a luminaire only as an IES file even when its manufacturer supplies an LDT. Converting it lets the target application use the fixture’s photometric distribution without remeasuring the luminaire.
What the LDT format is
LDT usually refers to EULUMDAT, a structured plain-text photometric format commonly stored with the .ldt extension. Luminaire manufacturers, photometric laboratories, DIALux, Relux, and other European lighting tools use it to describe a fixture’s light distribution.
An LDT can contain the manufacturer and luminaire name, dimensions, lamp or LED data, electrical power, luminous flux, photometric type, symmetry, measurement angles, and candela values. The format is common in manufacturer download libraries and European lighting workflows, but it is not limited to Europe.
The .ldt extension is not globally unique. Open the file in a text editor and confirm that it contains EULUMDAT records rather than binary or application-specific data before converting it.
What the IES format is
IES is a plain-text photometric format defined by the Illuminating Engineering Society and commonly distributed with the .ies extension. It is widely accepted by North American lighting software, CAD and BIM applications, rendering engines, and photometric catalogs.
An IES file records the lamp or LED count, lumens, dimensions, photometric type, angular intervals, and candela values in an LM-63 data structure. The exact LM-63 revision matters: older applications may require LM-63-1995, while newer software generally supports LM-63-2002 or LM-63-2019.
How to convert LDT to IES
Using Photometric Toolbox
- Install Lighting Analysts Photometric Toolbox, or use its current web-based Photometric Toolbox service when uploading the file is acceptable. Confirm that the edition supports EULUMDAT import and IES export.
- Open the
.ldtfile and inspect the luminaire dimensions, luminous flux, wattage, photometric type, mounting orientation, and intensity graph. Correct source data before exporting if the software provides editing tools. - Choose the program’s photometric export or save-as command and select
IES. Select the LM-63 revision required by the receiving application; use the oldest supported revision only when compatibility requires it. - Save the result under a new name such as
fixture-name.iesand retain the original LDT. - Open the IES file in the final DIALux, Relux, CAD, BIM, or rendering application. Compare its polar or Cartesian distribution with the source before using it in calculations.
Using DIALux, Relux, or LDT Editor
Some versions of DIALux evo, Relux, and DIAL’s free LDT Editor can import or inspect LDT files, but their export options vary by product and release. Import the luminaire, then look for Export luminaire, Save luminaire, or Export photometric data. Do not assume that an application that imports LDT can also create IES; if IES is not explicitly offered, use Photometric Toolbox or another dedicated photometric converter.
For a non-confidential file, a specialist vendor’s online converter can avoid installation; Lighting Analysts’ Photometric Toolbox web service is preferable to a generic file-conversion website because it is designed for photometric formats. Check that the service explicitly lists EULUMDAT and LM-63 support, download the output, and validate it in desktop lighting software. Do not upload proprietary manufacturer files, unreleased measurements, or project data unless the service’s privacy and retention terms are acceptable.
Quality and compatibility limits
Conversion transfers photometric data, not every field in the source. Manufacturer-specific comments, detailed LED information, tilt records, auxiliary metadata, and some descriptive fields may be omitted or rewritten. The converted IES also contains no three-dimensional luminaire model, so the target application may need separate fixture geometry.
Compare the source and output luminous flux, dimensions, peak candela, beam angles, symmetry, and photometric type. Pay particular attention to the measurement orientation: incorrectly interpreting A-, B-, or C-plane data can rotate the distribution even when the numerical intensities look plausible.
LDT and IES may use different conventions for flux normalization, angular grids, headers, and unit declarations. A converter may rescale candela values or interpolate angles while preserving the intended distribution. Recheck calculated illuminance, especially for asymmetric fixtures, narrow beams, wallwashers, and files with incomplete or unusual source metadata.
Suggested software and links: ldt to ies converters
Frequently asked questions
Is the LDT to IES converter free?
Yes, converting LDT to IES on 101convert.com is completely free. No registration, email address or installation is required. If you need a higher file size limit or want to convert more files at once, see our plans.
How large can my LDT file be?
You can upload LDT files up to 10 MB and convert up to 20 files at once in a single batch.
What happens to my uploaded files?
Files are processed automatically and deleted from our servers within a few minutes after conversion. We never view or share your files.
Do I need to install any software to convert LDT to IES?
No. The LDT to IES conversion runs entirely online in your browser and works on Windows, Mac, Linux, Android and iPhone.
Did the conversion fail?
In most cases, the cause is an incorrect file format. Please upload a valid LDT file for this LDT to IES conversion. Occasionally, the issue may be on our side. We analyze recurring conversion failures and disable or fix the converter if we detect a defect.
Does converting an LDT file to IES change the photometric data?
The luminous-intensity measurements should remain the same when the LDT angle grids, units, and candela values are mapped correctly. However, some descriptive or manufacturer-specific LDT fields may not have an equivalent in the IES format.
Will the luminaire orientation stay the same from LDT to IES?
It can change if the source coordinate convention is interpreted incorrectly, so the resulting IES file should be checked against the LDT's C-plane and vertical-angle definitions. A rotated distribution can produce incorrect lighting results even when the intensity values themselves are unchanged.
Why does the flux in my converted LDT to IES file not match?
A flux mismatch usually comes from different lumen fields, unit handling, normalization, or a candela multiplier being applied incorrectly. Compare the reported lumens and integrated intensity distribution, rather than assuming the two files use the same flux value automatically.
Can every LDT file be converted to IES without losing information?
Most standard photometric measurements can be transferred, but LDT metadata, special symmetry descriptions, and fields without direct LM-63 equivalents may be simplified or omitted. The IES result remains editable as structured photometric text, but it is not guaranteed to preserve every original LDT field.