DEFAULTLIGHTING system variable
Specifies whether default lighting should be used always or only in case no other lights have been switched on. Default lighting consists of distant light that follows the view direction. This setting can be specified per viewport. When default lighting is used, it replaces all other light sources defined in the drawing.
Off (0): Default lighting is used only in case no other lights are switched on
On (1): Default lighting is used instead of the light sources defined in the drawing