Light Filters are used to manipulate lighting results. In the real world this is often achieved through the use of stencils and gels to change the color, quality, and amount of light in a shot. RenderMan's light filters are a powerful and flexible way to do the same (and even more) in lighting your scenes.
Light Filters do not affect photon emission in the PxrVCM or PxrUPBP integrators.
PxrIntMultLightFilter is a light filter that allows you to multiply the intensity/exposure of the light. This is very useful when you want to isolate a particular asset(s) from the rest of the scene that has different intensity/exposure. This is via linking the objects to the PxrIntMultLightFilter.
PxrBarnLightFilter allows us to create physically accurate window barns to simulate the real set lighting with correct shadowing. Its other usage include controlling bounce lights in a large scene. In addition to the physical mode, it also provides an analytic mode.
PxrGoboLightFilter projects a painted texture in front of the light.
PxrCookieLightFilter projects a painted texture in front of the light. It's similar to the PxrGoboLightFilter but with more options and flexibility.
PxrBlockerLightFilter uses a "rod" like object to block light. The blocker can be shaped into an irregular shape and is then placed next to the object where you want to block the light.
PxrRodLightFilter uses a "rod" like object to block light. The blocker can be shaped into an irregular shape and is then placed next to the object where you want to block the light. This is similar to the above PxrBlockerLightFilter but with more controls and flexibility.
PxrRampLightFilter uses a ramp to control the light. This allows more complex control of color, intensity, and more.