eulumdat-ies

Bidirectional converter between EULUMDAT (.ldt) and IES LM-63-2002 (.ies) photometric file formats — part of the eulumdat-* ecosystem.

IES Type C only. Type A and Type B photometry are out of scope.

Installation

pip install eulumdat-ies

Command-line interface

# IES → LDT
ies-to-ldt luminaire.ies
ies-to-ldt luminaire.ies -o output/

# LDT → IES
ldt-to-ies luminaire.ldt
ldt-to-ies luminaire.ldt -o output/

Output files are written in the same directory as the source file by default, using the same stem: luminaire.ies → luminaire.ldt, luminaire.ldt → luminaire.ies.

Python API

from pyldt import LdtReader
from eulumdat_ies import ldt_to_ies, ies_to_ldt

# LDT → IES
ldt = LdtReader.read("luminaire.ldt")
ldt_to_ies(ldt, "luminaire.ies")        # write to file
ies_str = ldt_to_ies(ldt)               # or return as string

# IES → LDT
ldt = ies_to_ldt("luminaire.ies")       # from file path
ldt = ies_to_ldt(ies_string)            # or from string content

The Ldt object returned by ies_to_ldt is fully compatible with the entire eulumdat-* ecosystem (eulumdat-plot, eulumdat-luminance, eulumdat-ugr, etc.).

Format notes

LDT → IES

• Intensities converted from cd/klm to absolute candelas using lamp_flux × num_lamps / 1000
• If lamp flux is unavailable, lamp_lumens = -1 is written (IES convention for measured flux)
• All C-planes from the expanded LDT matrix are written (ISYM is transparent to the caller)
• C=360° is omitted if C=0° is also present (no duplicate)
• Dimensions converted from mm to metres

IES → LDT

• Intensities converted from absolute candelas to cd/klm
• If lamp_lumens = -1: values stored as-is, lamp_flux set to 1000 lm, warning emitted
• Matrix is always ISYM=0 — use eulumdat-symmetry to re-detect symmetry if needed
• C=360° duplicate stripped if present
• Negative IES dimensions (circular source) → positive millimetre values

Error handling

from eulumdat_ies import IESTypeError, IESParseError

try:
    ldt = ies_to_ldt("luminaire.ies")
except IESTypeError:
    print("Not a Type C file")
except IESParseError:
    print("Malformed IES file")

Ecosystem

eulumdat-py  (pyldt)
    └── eulumdat-ies  (eulumdat_ies)   ← this package

eulumdat-ies depends only on eulumdat-py. No NumPy, no external dependencies.

License

MIT