IES and LDT file validator

What is an IES file validator?

An IES file validator reads a photometric file the way a calculation program does and checks that its header, TILT line, angle lists and candela table are complete and consistent. It reports errors that will stop an import and warnings that should stop you, and this one also cross-checks the stated lumens against the light the candela table contains.

An IES file is plain text to IESNA LM-63: keyword lines in square brackets, a TILT line, thirteen header numbers (lamp count, lumens per lamp, multiplier, angle counts, photometric type, units, dimensions, ballast factor, watts), the angle lists and the candela values. An LDT file follows the fixed EULUMDAT layout with an intensity table in cd/klm. Both fail in the same ways: truncated tables, mis-typed counts and header figures pasted from another product.

Files are sent to NR Lighting's processing service for parsing and analysis; they are not published or added to any library.

How to use the IES and LDT validator

1. 01Drop an .ies or .ldt file onto the upload area, or click to browse; the format is detected from the content, not the extension.
2. 02The file is parsed on NR Lighting's servers against LM-63 or EULUMDAT and returned with errors, warnings and a photometric summary.
3. 03A file that cannot be parsed shows 'File could not be parsed' with the first structural error; a file with issues loads and shows the first warning.
4. 04Compare the parsed manufacturer, luminaire name, watts, flux, dimensions and efficacy with the datasheet, or open the Raw tab to read the text.
5. 05With NR Lighting Pro, open Sanitize for the itemised report and repair options.

The method: what the validator checks

Φ = Σ Ī(zone) × 2π × (cos θ1 − cos θ2) × multiplier. Difference = (Φ integrated − Φ rated) ÷ Φ rated × 100 %. Within tolerance when |difference| ≤ 15 %.

Structural checks run first. The parser strips byte-order marks, normalises line endings and decimal commas, locates the TILT line (or searches for the data block when it is missing), reads the thirteen header values, the angle lists and the candela table, and counts everything against what the header promised. Out-of-range or out-of-order angles are corrected in memory so the flux check can still run, and the correction is reported as a warning.

The flux check integrates the candela table zone by zone with the Type C relationship above, applies the LM-63 multiplier and compares the result with the stated luminaire flux where given, otherwise with the rated lamp flux.

Worked example

A 3000 K retail downlight arrives as an IES file: one lamp, 2,000 lm per lamp, multiplier 1, 21 W, Type C, 37 vertical angles (0 to 180° in 5° steps) and 5 horizontal planes (quadrilateral symmetry), so 37 × 5 = 185 candela values are expected and 185 are found. TILT=NONE and the LM-63-2002 keywords are present: no structural errors.

Zonal integration gives 1,840 lm. Difference = (1,840 − 2,000) ÷ 2,000 × 100 % = −8.0 %, inside the ±15 % tolerance, so the file loads without a flux warning; the gap is a 92 % light output ratio for a reflector downlight with a glass. Efficacy is 95.2 lm/W on rated lamp flux (2,000 ÷ 21) and 87.6 lm/W on luminaire output (1,840 ÷ 21), the form Approved Document L uses.

Now suppose lumens per lamp was hand-edited to 1,500 lm for a lower drive current with the candela table untouched. The integrated 1,840 lm exceeds 1,500 × 1.15 = 1,725 lm, so the validator warns that the calculated luminaire flux exceeds the rated lamp flux, which is physically impossible: the file's data may be corrupt. That is the file that would quietly over-light a Dialux model.

Free checks and Pro repair

Validation runs on every upload and needs no account. The free editor shows the parsed values, lets you edit header fields in the browser and read the raw text; downloading an edited file is a Pro feature. NR Lighting Pro adds the Sanitize tab, which lists every critical error, potential issue and recommendation with the angle counts and header keywords, then repairs what can be repaired: a missing IESNA:LM-63-2002 version line, the [MANUFAC] and [LUMCAT] keywords (manufacturer and catalogue lines in an LDT) and the lumens-per-lamp value. Each change is listed and the file downloads with a _repaired suffix.

Limitations, and when to involve a lighting designer

The validator checks that a file is well formed and internally consistent. It cannot tell whether the photometry is right for the product specified: a file can pass every check and still describe a different optic, colour temperature or drive current from the datasheet. The flux check assumes Type C geometry, so Type A and B results are approximate and flagged. The repair cannot rebuild a truncated candela table, re-order angles or create a missing TILT line; a file whose data block cannot be located must go back to the manufacturer. Nothing here is a compliance sign-off: BS EN 12464-1 and the SLL Code for Lighting judge the calculated installation, not the file.

I check every photometric file before it goes into a calculation model. If you are assessing a substitution at tender, working from files of uncertain provenance, or designing accent lighting where beam data decides the result, as in the showrooms and retail interiors NR Lighting works on, get in touch.