Talking BasicEffects, where is the source of the three directional lights?
When I write this:
effect.DirectionalLight0.DiffuseColor = new Vector3(0.5f, 0, 0); // a red light
effect.DirectionalLight0.Direction = new Vector3(1, 0, 0);
What does it mean for the direction? From where is it directing?
Directional lights have no position. Think of the sun lighting objects on earth. Technically it has a position, but it is so far away that it does not matter.
Therefore a directional light will illuminate based only on the angle between the light's direction and the surface normal.
If you want lights with a position that also have attenuation, you want to use point lights.
