In order to apply a filter to a light, it must be set as a child of that light. Alternately, a light filter reference can be put in place as a light child; it will act as a filter proxy. To set the filter as the light child, simply middle-click and drag the light filter on the light, in the Gaffer Object Table. To use a light filter reference as a proxy: Using a light filter reference allows sharing one filter with several light sources.Alt+F
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