Octane will use the global light values from this tab as long as there are no other light source(s) in the scene. This global light has no special features. It only provides artificial, indirect lighting to the scene (figure 1).
Figure 1: The Environment Light settings located in the Environment tab.
Luminance Mult.
If a Cinema 4D material in the scene has its Luminance channel active, its strength can be increased or decreased with this option (figure 2).
Figure 2: Adjusting the Luminance Multiplier.
Env. Color
Adjusts the global environment light color (figure 3).
Figure 3: Changing the Environment Color.