GAMGI Tutorials: Directional and positional lights

Select Light->Modify, and press the mouse on the drawing area. A menu pops up, showing two menu items, for the two lights available. After choosing the first light, confirm its properties, in particular the new light direction, position, and angle, that were changed with the mouse.
Set Specular to (0.6, 0.6, 0.6) and press Ok. A bright spot is now visible at the center of the atom, due to the reflected light.
Select Light->Config and set Shininess (Materials page) to 0.0. After pressing Ok the bright spot disappears. Repeat the operation, this time set Shininess to 0.5. After pressing Ok the bright spot reappears, much brighter now, as the material light reflectance was increased.

Select Light->Modify, and press the mouse on the drawing area. A menu pops up, showing two menu items, for the two lights available. After choosing the first light, set angle back to 90.0, color Ambient to (0.6, 0.6, 0.6), Specular to (0.0, 0.0, 0.0) and press Ok. The initial full color atom circle returns.
This happens because the absence of lights correspond in fact to the existence of a light with Ambient component set to (1.0, 1.0, 1.0), and Diffuse, Specular components set to (0.0, 0.0, 0.0), the maximum luminosity that can be achieved. As the light components of the two lights are added, the total ambient light is now (1.0, 1.0, 1.0), so the maximum luminosity has been already reached and additional diffuse light cannot increase further the luminosity.

Select Atom->Modify and press the mouse over the atom. After confirming the atom properties, set Style to Wired and press Ok. The atom is now shown as a cross.
Press Light->Modify and press the mouse over the graphic area. A menu pops up, showing two menu items, for the two lights available. After choosing the first light, confirm its properties, set Ambient to (0.0, 0.0, 0.0) and press Ok. Repeat for the second light, so the total ambient light is now (0.0, 0.0, 0.0). Because wired objects cannot reflect diffuse or specular light, they require ambient light to be visible. As the ambient light has been switched off, the wired cross becomes barely visible.
Select Light->Remove and press the mouse over the graphic area. A menu pops up, showing two menu items, for the two lights available. Choose the first light, then the second, to remove them. The wired cross is visible again.