the question is where is north in your case ? below just gets the polar coordinates from the light direction vector xy components. It starts rotation at the x axis and rotates counter-clockwise, so y-axis would be 90 degree:
import scriptcontext
import rhinoscriptsyntax as rs
from math import atan2, degrees
def DoSomething():
ids = rs.ObjectsByName("MySun", select=False, include_lights=True)
if not ids: return
if not rs.IsDirectionalLight(ids[0]): return
direction = rs.VectorReverse(rs.LightDirection(ids[0]))
deg_angle = degrees(atan2(direction[1], direction[0]))
if deg_angle < 0: deg_angle += 360
print deg_angle
DoSomething()
does that help ?
c.