https://renderman.pixar.com/resources/18/rps/geometricAreaLights.html https://renderman.pixar.com/resources/18/rps/geometricAreaLi... I haven't looked to deeply

https://renderman.pixar.com/resources/18/rps/geometricAreaLights.html https://renderman.pixar.com/resources/18/rps/geometricAreaLi... I haven't looked to deeply, but I'm pretty sure it's just a refinement of their older techniques.