The IES Sun and IES Sky objects are photometric light objects that simulate the sun and sky. IES stands for Illuminating Engineering Society; see IES Standard File Format.
IES Sun is a physically-based light object that simulates sunlight. When used in conjunction with a daylight system, its values are set automatically based on geographic location, time, and date. (IES stands for Illuminating Engineering Society; see IES Standard File Format.)
IES Sky is a physically-based light object that simulates atmospheric effects on skylight. (IES stands for Illuminating Engineering Society; see IES Standard File Format.)