Basically, I'm wondering if I can set the sun lamp's light direction towards a position, such as an object, with a simple command, rather than doing rotations with R which is hard to control.
One way to do this is with a Track To constraint:
- Select the sun lamp
- ⇧ Shift select the object you wish to point the lamp at
- Press ⎈ CtrlT and choose Track To Constraint.
The sun lamp will now always "look" at that object, so you can move it around with G for easy adjustment.
You can adjust the constraint (or remove it) in the Constraints tab of the Properties area when the sun lamp is active: