Image courtesy of Mihai Illuta. Ajax model courtesy of Jotero
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Both formats contain the luminous intensity at any angle, measured in laboratory using light sensors located all over a spherical dome around the light source, pointing to the center of the dome so that the data capture method considers all lamps as point sources. This means that with these formats, the physical correctness of the result is highly dependent on the geometry you apply the IES/ Eulumdat files to.
You can use IES/EULUMDAT emitters with any type of geometry but for the most predictable results it is recommended you apply it on a small sphere. The intensity of the .IES/.EULUMDAT light itself is already specified in the file - normally you shouldn't need to change it for realistic results. But you can adjust the intensity if you wish using the Intensity parameter which acts as a multiplier for the built-in intensity of the .IES/EULUMDAT file. You can also change the intensity using Multilight, but keep in mind that Color Multilight is not compatible with this type of emitters.
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