NVIZ: LIGHTING PANEL

Lights settings are stored in the Lighting Panel: this panel contains adjustments and options to control the position, color and brightness of the lights and the reflectivity (shininess) of the surface.
Clicking on the menu Panel -> Lights, the Lighting Panel will appear under the Generic Panel:

On the Generic Panel set zexag to 3 and fit image size to screen with perspective.
With the Show Model checkbox you can visualize the sphere showing current lighting effects: select it if it's not selected and set Brightness to the maximum value by moving the scroll bar to the left. The sphere in the center of the screen is almost black because observer's eye and sun position have the same direction (South-East).

With the directional panel (the one of the Lighting Panel, in the right bottom corner of the form) move sun position to North-East.

  DIRECTIONAL PANEL

In this way the sphere is gaining brightness and shades are changing position:

Move Brightness scroll bar once again and see how the effect on the sphere is changing, then set it to 0.8.
Do the same with Ambient (this command regulates contrast): move the scroll bar from the minimum to the maximum value and finally restore the original value.
Red, Green and Blue scroll bars adjust the Red, Green and Blue components of the main light: now set Green to 0.1 Blue to 0.2 and Brightness to 0.5 to see a sunset-like light effect.

Reset Green and Blu values to 1 and Brightness to 0.8.
Height scroll bar sets sun height (vertical distance from the surface): move it from 0.1 to 1 checking the variations on the sphere. Next image has Height value set to 0.1.

Set Height to 0.8 and move the sun with the lighting directional panel untill you reach the South-East direction, then move the observer to North-West, this time using the directional panel of the Generic Panel: the sphere is not yet dark because observer and sun have not the same direction.

Finally move the observer to South-East and click on Follow ViewPoint button: checking this option will make the light follow the viewers' position. Adjusting the Height or XY position (with the directional panel) of the light automatically toggles Follow Viewpoint off.
Now move the observer to North-West and you will note that sun direction moves too.