IES file
Every line of an IES file: what it means and where the value comes from.
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Plain-language guides to photometric files and diagrams.
Start here
New to photometric files? Read the pages in this order: IES file, LDT file, IES and LDT compared, dimensions and orientation, and then the diagrams.
File formats
LDT file
Every line of an LDT (EULUMDAT) file: what it means and where the value comes from.
IES and LDT compared
One luminaire in both formats, why a correct pair is turned by 90°, and how to check a pair.
Dimensions and orientation
Which way the luminaire faces, and how to measure length, width, and height for ten luminaire types.
Diagrams
Polar diagram
How the intensity curve shows where the light goes, and how much.
Cone diagram
How wide the light spot is, and how bright, at each mounting height.
Isolux diagram
A map of the light on the floor below one luminaire.
Diagram styles
The decisions behind the look of a diagram: typeface, colour, line weight, and scale.