If you place a PointLight inside of the cube, the cube won’t be lighted from inside.
Workarround 1: use different light e.g. HemisphericLight
Workarround 2: use several PointLights outside of the cube: if you point the light on a cube from outside, it will light also from inside (actually this is also a bug)
Indeed, the normals are pointing to the outside. If you want the lighting to also work inside the cube, you can set the twoSidedLighting property of the material: