The Unity® Directional light source cannot function independently like the Point light, Spotlight, or Area light. It works in conjunction with either a Daylight or Texture environment, which you specify in a PBR Render Target under the Environment rollout (Figure 1).
Figure 1: The Directional light is used in conjunction with either a Daylight or Texture environment
Due to the nature of a Directional light, the only Unity parameter compatible with OctaneRender® is Intensity.