Octane will use the global light values in this section as long as you do not put the light source(s) on the scene. This global light has no special features. It only gives artificial and dull lighting to the scene, at least you control how your scene looks until you use real light sources. There is no other function than that.
If you are using Cinema 4D material in your scene and you have used the Luminance channel in the material settings, you can increase or decrease its brightness with this option.
DEFAULT ENVIRONMENT COLOR:
Here you can adjust your global environment light color. This option is automatically deactivated when you start using another light source.
Info: The default environment is now saved as a parameter in the scene. So when you reopen your scene, the color you define here is loaded.