[Radiance-general] calculation of one reflection (rtrace)

[Robert Franke]

Hi,

I try to understand how RADIANCE calculate the radiance values, but the 
specular value for one reflection isn't clear.
I understand, that  the diffuse value is independent of view. On point 
P_r=(0 1 1)  I got from rtrace for the red channel 0.22361, I calculated:

R_r_light=100
sphere_radius=0.5
distance=2.2360
rho_surf1=0.1
cos(63,43) = light incoming angle

R_r(0,1,1) = R_r_light * (sphere_radius)² / (distance)² * cos (63,43) * 
rho_surf1 = 0.223606797.

Ok, this value is fine, but what will happen if I look from (0 -1 1) to 
(0 1 -1) at point (0, 0, 0), I thought  this, but it didn't work:

distance=3
rho_mirr=0.3
diff=0.9
spec=0.1
cos(45) = reflected light - observer angle
P_r=0.22361

R_r(0,0,0) = R_r_light * (sphere_radius)² / (distance)² * rho_mirr * 
diff + spec * P_r * cos(45) = 0.765811388

rtrace = 0.76517

Can somebody explain how the specular component is calculated on my test 
scene? I do not get it...

Here is my test scene:

######materials.rad######
void plastic mirr
0
0
5 .3 .2 .1 0.1 0

void plastic surf1
0
0
5 .1 .1 .1 0 0

void light lighty20
0
0
3 100 150 200

######test.rad######
mirr polygon plate1
0
0
12
-1 -1 0
  1 -1 0
  1  1 0
-1  1 0

surf1 polygon plate2
0
0
12
-1  1 0
-1  1 3
  1  1 3
  1  1 0

lighty20 sphere light_s
0
0
4 0 0 3 0.5