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.
To add a light filter to a light, first create a light filter from the Add menu:
Next, select the light you want to be filter, and look at the object properties panel. You should see a Light Filters panel.
Click the + to add a new entry, then select which light filter object you want to link to.
You can also use the shortcut in the object context menu. Select the light you want to filter and select the light filter you want to add from the Attach New Light Filter menu. The new light filter will automatically be added to the light filters list.
For detailed information about parameters, follow the links for each light filter type.