Light Settings in the 3D View form may be toggled on and off with the light bulb icon 
shown in the menu bar. This function allows the user to define the direction and intensity of the light source.
When the box Light On is checked, it is able to hold and move the red dot in the compass to change the light direction. The user may also adjust the properties of visible light such as ambient, diffuse, specular and global.
Figure 1. 3D View: Light Options.