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— Glossary · Technical

IES / LDT Photometric File

An IES file (IESNA LM-63 format, or the European LDT/EULUMDAT equivalent) is the digital photometric fingerprint of a luminaire: a table of luminous intensity in every direction, measured on a goniophotometer. It is what lighting design software such as DIALux and AGi32 consumes to predict lux levels, uniformity and glare on a real layout before anything is bought or mounted. A rendered brochure image proves nothing; an IES file lets an engineer verify that a claimed 60° beam actually is one, and simulate the exact fixture on the exact site geometry. Any serious industrial lighting supplier provides IES/LDT files on request for each fixture and optic variant — and refusing to share them is a red flag worth acting on.

In practice
See flood lights with measured photometric data and IES files
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