$initialanglerange

$initialanglerange is deciding the photon emission angle. The scale is from 0 to $2\pi$.

$initialanglerange
${\theta }_{start}$  ${\theta }_{end}$

The initial photon emission angle range is decided by

$v_x=sin(\theta )$  
$v_y=cos(\theta )$  

And theta is within ${\theta }_{start}<\theta <{\theta }_{end}$

The $initialanglerange setting in GUI interface is here
Press Ray Tracing and fill in the field for the Emitting angle as needed!