In the arial view you can place a light fixture. While there you will need to associate the light to a wall. Click into elevation view. click on light fixture once. You can then move the light anywhere you want to . I use a laptop without a mouse so I hold shift and left button and use the down arrow key. With a mouse I am not sure how to move it down. Probably click and hold the left mouse button and move it, I guess. hth.
Stupid me . In the elevation view you can click on the fixture then click on the box up to the left that says bottom. You can type in the distance from the floor and it will move there. I guess that would be much easier than the way I said in the previous post. I know the picture I have here are not in elevation view but I wanted to show you the difference.