in sky.cpp add that at line #86

	sun = mgr->addLightSceneNode(this,
		core::vector3df(0,10000*BS*2,0),
		video::SColorf(1.0f, 1.0f, 1.0f, 1.0f), 30000);
	video::SLight *ldata = &sun->getLightData();
	ldata->AmbientColor = video::SColorf(0.2f, 0.2f, 0.2f, 1.0f);

you will set up light source for our world.

now set materials in mapblock_mesh.cpp #1202:

material.setFlag(video::EMF_LIGHTING, true);

now you have ligths enabled

start the game without shaders: you will see that world is lit by the source

enable shaders now,

world is not lit by light source, it still works on vertex colors we have set.

conclusion: when you are using default materials, irrlicht is adding own shaders

when you are modyfing them you have to do your own light calculations.
All the lightsource data are passed into your shader. Pos, ambient, specular etc.