When specifying photometric properties for a lighting fixture, set the light distribution to Photometric Web, and use the manufacturer’s IES file, if one is available. Because an IES file provides a more accurate representation of the light source, you get better results in a rendered image.
To obtain an IES file, go to the website of the lighting manufacturer, and search for ies. Locate the IES file for the desired lighting product, and save it to your computer. See Specifying an IES File for a Light Source.