diff -urN rt_v2/cg.py rt_v3/cg.py
--- rt_v2/cg.py	2018-03-17 19:20:42.000000000 +0900
+++ rt_v3/cg.py	2018-03-18 10:31:07.000000000 +0900
@@ -29,6 +29,10 @@
 		'l2g': [ ax.zoom_all(20) ],
 	} ]
 
+	lights = [
+		{ 'v': [0,0,-1], 'e': 1.0 },
+	]
+
 	(w, h) = ( ut.arg_i('w', 640) , ut.arg_i('h', 480) )
 	div = ut.arg_i('div', 1)
 	(w, h) = map( lambda v: v / div, (w, h) )
@@ -58,7 +62,7 @@
 		f = rt.draw
 		if 'wf' in sys.argv:
 			f = wf.draw
-		f(data, eye2g, wh2eye, sc_sz, video)
+		f(data, lights, eye2g, wh2eye, sc_sz, video)
 
 		video.add_img()
 		fn = ( name if n == 1 else name+'0000{}'.format(i)[-5:] ) + '.jpg'
diff -urN rt_v2/rt.py rt_v3/rt.py
--- rt_v2/rt.py	2018-03-17 19:19:33.000000000 +0900
+++ rt_v3/rt.py	2018-03-18 10:57:44.000000000 +0900
@@ -10,15 +10,44 @@
 	def_col = d.get( 'def_col', v.all(128) )
 	return def_col
 
-def get_col(data, l_g):
+def diffusivity(lights, crsp, nv, eyev_nega):
+	ang_nv_eye = v.dot_product( nv, eyev_nega )
+
+	def f(ltd):
+		ltv = [0,0,1]
+		if 'v' in ltd:
+			ltv = v.nega( ltd.get('v') )
+		elif 'p' in ltd:
+			ltv = v.sub_unit( ltd.get('p'), crsp )
+		ang_nv_lt = v.dot_product( nv, ltv )
+		if ang_nv_eye * ang_nv_lt < 0:
+			return 0
+		return max( ang_nv_lt, 0 ) * ltd.get('e', 1.0)
+
+	return sum( map( f, lights ) )
+
+def get_col(data, lights, l_g):
 	lst = map( lambda d: ( d, cross.cross_g(l_g, d) ), data )
 	lst = filter( lambda (d, crs): 't' in crs, lst )
 	if not lst:
 		return []
 	(d, crs) = min( lst, key=lambda (d, crs): crs.get('t') )
-	return map_col(d, crs)
+	col = map_col(d, crs)
+
+	rt = d.get('rt', {})
+	base = rt.get('base', 0.3)
+
+	crsp = crs.get('p')
+	nv = v.unit( crs.get('nv') )
+	eyev = v.unit(l_g.v)
+	eyev_nega = v.nega(eyev)
+
+	diff = diffusivity(lights, crsp, nv, eyev_nega) * rt.get('diff', 0.9)
+	col = v.op1( '*', col, base + diff )
+
+	return map( lambda v: min( int(v), 255 ), col )
 
-def draw(data, eye2g, wh2eye, sc_sz, video):
+def draw(data, lights, eye2g, wh2eye, sc_sz, video):
 	(w, h, d_) = sc_sz
 	wh2g = lstx.opt( wh2eye + [ eye2g ] )
 	cnt = ut.new_cnt_wh(w, h, 'wh')
@@ -26,7 +55,7 @@
 		(ix, iy) = cnt.cur()
 		p = lstx.tr( wh2g, 'l2g', [ix,iy,-d_] )
 		l_g = line.new_p2(eye2g.p, p)
-		col = get_col(data, l_g)
+		col = get_col(data, lights, l_g)
 		if col:
 			video.set(ix, iy, col)
 # EOF
diff -urN rt_v2/wf.py rt_v3/wf.py
--- rt_v2/wf.py	2018-03-16 20:50:41.000000000 +0900
+++ rt_v3/wf.py	2018-03-18 10:29:07.000000000 +0900
@@ -70,7 +70,7 @@
 		(pa, pb) = r
 	return [pa, pb]
 
-def draw(data, eye2g, wh2eye, sc_sz, video):
+def draw(data, lights, eye2g, wh2eye, sc_sz, video):
 	col = v.all(255) # white
 	for d in data:
 		ps = []