Well the grandest of all places under mountain Kazad-um, later called the dreaded mines of Moria once the sleeping Balrog was awakened and drove the dear dwarves out, was illuminated at the upper level I believe by three windows high on the eastern side which let the light in very wellThen the other levels down it seems that the dwarves hung crystal lamps from the ceiling and the halls were greatly and awesomely lit with this crystal light. I should have loved to see that for myself.
Hi Gildor. Not sure re heights.... However I believe that Durin's tower was built as a look out over possibly dangerous land during the Elder Days. The Dwarves could keep an eye on the goings on in Middle Earth without actually leaving Moria. The tower would have been totally unassailable due to its height. It was reached by a spiral stair way carved from the living rock, from the depths of Moria depths to the heights and jutted out at almost the very top of the mountain. What an amazing view it would have been.
Re illumination I remember reading about lamps hangings from the ceilings and light shafts cunningly carved to that they let in light and fresh air. I suppose a good example of these would be the light shaft which shone directly onto Balin's tomb in both book and film.