$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!