You can position the active light by clicking and dragging directly on the model in the Render View.
We call this positioning method LightPaint. The LightPaint tool uses the LightPaint mode seledcted to calculate the new position of the light.
•Reflection (Keyboard shortcut: Ctrl-1) - in this mode, the light is positioned to reflect at the point on the surface (P) where you clicked.
•Illumination (Keyboard shortcut: Ctrl-2) - in this mode, we calculate the normal to the surface of the object at the point where you click (P) and then position the light source along that normal. This is best for lighting diffuse objects where you are not concerned about the reflections of lights but simply want to shine a light directly at a surface.
•Rim (Keyboard shortcut: Ctrl-3) - in this mode, the model is ignored allowing you to position lights behind the model.
Diagram showing the 3 LightPaint modes, Reflection, Illumination, Rim