As the distance increases further from the light source, we integrate over less rays for finding the radiance.
xinwei-zhuang
how do we handle if $$\theta=90$$?
micahtyong
@Xinwei, if theta = 90, that means a light ray is hitting at a 90 degree angle to the surface unit, A. Intuitively, it should be impossible for a light ray to hit A from that direction. Think about using a laser pointer to hit A from a 90 degree angle. It should be impossible for the laser pointer to hit A! So, I think the behavior is undefined.
As the distance increases further from the light source, we integrate over less rays for finding the radiance.
how do we handle if $$\theta=90$$?
@Xinwei, if theta = 90, that means a light ray is hitting at a 90 degree angle to the surface unit, A. Intuitively, it should be impossible for a light ray to hit A from that direction. Think about using a laser pointer to hit A from a 90 degree angle. It should be impossible for the laser pointer to hit A! So, I think the behavior is undefined.