Either three ranges of windows, one above the other, on either side of the house; or perhaps the three ranges were one in either side wall, and the third in a wall down the middle of the hall, along the course of the midmost row of pillars. The windows were directly opposite one another, giving what we call a through light.
Related Commentaries of 1 Kings 7:4
1 Kings 7:4
4 And there were windows in three rows, and light was against light in three ranks.