What should I check before importing an IES or LDT file?

Match the file to the manufacturer, exact model, optic, output setting and test reference. Check how the software interprets flux, watts, luminous dimensions, units and orientation. Review warnings and preserve the original file before making changes. Start with one luminaire in a simple layout so incorrect direction or unexplained scaling is visible before the file is repeated throughout a project.

What is the difference between IES and LDT files?

IES files use the LM-63 transfer format, while LDT files normally use EULUMDAT. Both can convey luminaire photometry, but their field structures and conventions differ. Do not judge quality by the extension or assume the same field has the same meaning. When converting a file, compare interpreted output and distribution with the source and confirm that the target software supports the supplied data.

Does a value of −1 in an IES file mean it is damaged?

Not necessarily. In the lumens-per-lamp field, −1 identifies absolute photometry rather than a negative light output. The luminous output is obtained from the intensity distribution instead of using an editable rated-lamp value. Confirm which field contains the number and inspect the software’s interpretation. This IES marker should not be used as a universal rule for LDT, which has a different absolute-photometry convention.

How can an extra multiplier affect calculated illuminance?

An extra multiplier increases the represented directional intensity even though the installed luminaire has not changed. In an assumed point-source example at normal incidence, 10,000 cd at 5 m produces 400 lx. Applying an unjustified additional factor of 1.20 produces 480 lx, 20% too high. This is a direct-light arithmetic illustration, not a product test, whole-venue prediction or lighting requirement.

How do I check the orientation of asymmetric photometry?

Identify the reference plane and distribution direction in a photometric viewer, then relate them to the physical mounting arrangement. Place one luminaire in a simple layout and confirm which side receives the stronger light. Record the model’s orientation and aiming settings. Do not assume that similar housings share the same laboratory alignment or that a visually plausible render confirms the correct direction.

Should I accept an automatically repaired photometric file?

Review what was changed and why. A repair can alter a factor, angle set or other field to make a file readable, but it cannot reconstruct missing measurements reliably. Retain the original and the warning log. If the file is truncated, its configuration is uncertain or required supporting data is absent, request corrected data from the manufacturer before relying on the calculation.

Can an IES or LDT file prove all luminaire performance claims?

No. The file supports the photometric calculation for the represented configuration. It does not by itself establish flicker behaviour, environmental durability or compliance of the completed installation. Check separate reports for the required characteristics and compare the as-built equipment and settings with the approved schedule. A case photograph provides application context, while the corresponding data and commissioning records support specific technical conclusions.

IES and LDT Files: Checks Before Import

2026-10-27

Contents

1. Match the File to the Exact Configuration
2. Check Absolute Photometry and Output Scaling
3. Confirm Direction, Units and Luminous Dimensions
4. Validate the Imported Data Before Repeating It
5. Connect the File to the Installed Lighting
6. Technical Sources

1.Match the File to the Exact Configuration

A contractor imports a file named “1000W floodlight” and starts the layout. The software accepts it, but the quotation specifies a different optic. The model now answers the wrong question. Before using IES and LDT files, match the manufacturer, model, optic, output setting and test reference to the proposed equipment. Keep the original file with its issue date or revision.

Illustrative lighting designer comparing printed polar curves with photometric data on a desktop monitor — Check the file before modelling

IES LM-63 and EULUMDAT, commonly supplied as LDT, transfer photometric data for calculation. Neither extension certifies a project. Start with the CPS Download Center, then request the exact configuration if its file is unclear. Even a named product such as the Dubhe 1000W floodlight needs a confirmed optical version, not a generic file selected by wattage.

2.Check Absolute Photometry and Output Scaling

An IES file may show −1 in the lumens-per-lamp field to identify absolute photometry. That marker does not mean negative light or a corrupt file. LDT handles absolute data through a different convention, described by DIAL and Lighting Analysts. Check the software’s interpreted luminaire lumens and input watts against the matching report. Do not copy one format’s field rules into the other.

Check whether output scaling is already included before applying another factor. For an assumed point source at normal incidence, 10,000 cd at 5 m gives E = I ÷ d² = 400 lx. An unjustified extra factor of 1.20 gives 480 lx, a 20% overstatement. This simplified direct-light example excludes reflections and is not a site target. Keep output settings separate from maintenance losses.

Assumed point-source example shows an extra factor of 1.20 changing 10000 candela to 12000 and calculated direct illuminance from 400 to 480 lux at 5 metres — One multiplier changes the result

3.Confirm Direction, Units and Luminous Dimensions

After checking output, inspect the polar curve and photometric orientation. AGi32 warns that laboratory alignment can differ between similar luminaires. Identify the reference plane, then connect it to the physical bracket and aiming schedule. An asymmetric distribution rotated sideways can move light away from the intended area. The CPS floodlight aiming guide explains the resulting hot spots and weak zones.

Check dimensions with the same care. IES luminous dimensions can use feet or metres, while EULUMDAT has its own dimensional fields. Separate the luminous opening from the outer housing. Also distinguish photometric type and symmetry from physical tilt. In an IES file, TILT data describes an output correction associated with lamp orientation. It does not replace positioning and aiming the luminaire in the model.

Check	What to record	Why it matters
Product identity	Match model, optic, output setting and test reference.	A shared housing or wattage does not identify a distribution.
Output factors	Record the imported basis and any extra factor, such as 1.00 or 1.20.	An unexplained multiplier can change every calculated value.
Direction	Confirm the 0° reference plane and physical mounting orientation.	A sideways asymmetric beam may still look plausible on screen.
Dimensions and units	Check luminous dimensions and units, including metres versus feet in IES.	A luminous aperture is not necessarily the housing outline.
Data integrity	Resolve missing angles, candela values or referenced tilt data.	A repaired file can open without proving the measurements are correct.

4.Validate the Imported Data Before Repeating It

Review import warnings before copying the luminaire across the site. Photometric Toolbox documents missing tilt files, truncated candela tables and invalid factors as possible problems. Automatic repair may make a file readable by changing values, but that action does not establish what the laboratory measured. Obtain corrected data from the manufacturer when the underlying information is missing, and retain the warning record.

Place one luminaire in a simple test layout. Check the distribution direction, output, dimensions and settings before building the full DIALux or AGi32 simulation. If converting between IES and LDT, compare the interpreted flux and distribution before and after conversion. A successful import cannot establish flicker performance, corrosion resistance or every colour-quality claim. Request the separate evidence needed for those requirements.

5.Connect the File to the Installed Lighting

The CPS Sitong badminton hall case describes a 13-court venue upgraded to 102 luminaires rated at 150W, with optical calculations and commissioning. It shows why the selected configuration and layout belong together. The published page does not supply the complete configuration-linked photometric dataset, so its photograph cannot validate a file for a different hall. Request the data for the equipment being proposed.

Players on a blue badminton court beneath ceiling-mounted luminaires in the image published with the CPS Sitong retrofit case — Published Sitong badminton court image

Finish with a short file register containing the original filename, supplier confirmation, model and optic, test reference, imported output and any adjustments. Carry that identity into the lighting calculation report and final equipment schedule. This record makes later substitutions easier to review. IES and LDT files become useful design inputs when their identity, scaling and direction remain traceable through installation.

6.Technical Sources

Keywords: IES and LDT files, photometric file import, IES file, LDT file, absolute photometry, candela multiplier, photometric orientation, lighting simulation.