Photometric lights use data measured from real-world lights, often directly from bulb and enclosure manufacturers themselves. You can import IES profiles from companies such as Erco, Lamp, Osram, and Philips; their IES files provide accurate intensity and spread data for a given light model.
Example IES lighting profiles
As well as the settings that are common to all lights, the Photometric Light also has this parameter.
Allows you to choose an IES light profile that defines the distribution of light.
If not found in the default path, photometric IES files are searched for in texture_searchpath too.
Many IES files originate from various lighting manufacturers, some of whom put extra text at the beginning of their IES files. If you are experiencing difficulties rendering a particular IES file, try opening the IES file in a text editor and deleting the header text from the top of the file. The file should typically start with
TILT=NONE and if it doesn't, that may be the culprit.