Of course it's possible, but not at the same time, or actually that is also with some little tricks with 2 light sources.
I had in the previous gamelib demo with the mayan pyramid 2 invisible 3d area colliders which changed the ambientlight to 0 and 0.3. But that works only if the dark area is hidden behind a corridor corner inside a building, because else you would see the bright ambient inside the building from outside too.
The 2 light source method works better, but is also a bit more expensive in FPS. You set ambientlight to 0, and you have your normal directional light, and then you have a movable directional light without shadows following the camera, and pointing towards the main directional light.