When using the Surface Map and Surface Normal, new options become available on the Light Shader node and Tone Shader node. These options can be found in the new Surface tab of the nodes.
When using the Surface Normal node with the Light Shader or Tone Shader, the shader is able to light relative to the Z-position of the light and the elevation of the surface in the scene. This also allows for the addition of a specular highlight on the lit surface.
The original diffuse lighting from the Light Shader. The diffuse-style of lighting is created by calculating the amount of light being absorbed by the surface by using the direction of the light and the orientation of the surface.
The specular highlight helps to define shinier surfaces and is often used to emphasize more rounded surfaces. The specular-style of lighting is created by calculating the amount of light being reflected off of the surface and into the camera.
To learn more about the Specular Options check out the Light Shader and Tone Shader reference.
Now that the Light and Tone nodes are using field units in the scene, the light can fall-off as it recedes into the distance. When using the fall-off property, the brightness of a surface is calculated based on its distance from the light source. The light is at full strength at the Light Position node’s source and falls off, becoming less powerful, as it recedes towards the target.
The fall-off defines the percentage falloff at the weakest part of the light, the Light Position’s target. A value of 100% in the fall-off property will cause the light to fall-off completely, and no longer light the surface. The value of the rendered light is determined by the power of the light ray at the point that it intersects the surface.
The fall-off value can also be used to make the surface appear brighter when closer to the light. When the falloff is turned on with a value above zero, a light directly near the surface appears brighter and more direct than a light further from the surface.