Graphics Reference
In-Depth Information
What if we want to light the object in only one direction (Plane and Spheroid in front) with a
mesh-light? Is there a way to make a light-emitting plane emit light only from one side and
not the opposite side? Yes, there is; follow these steps:
1.
Open the
01_meshlight.blend
file, which has prepared the scene used for the
preceding screenshots, and be sure to enable only the first and the seventh layer.
2.
Put the mouse cursor on the left vertical 3D view, and press
Shift
+
Z
to navigate
in Rendered view mode.
3.
Click on the Emitter item in the Outliner to select it (if not already selected), and put
the mouse pointer in the Node Editor window. Add a Mix Shader node (press
Shift
+
A
and navigate to Shader | Mix Shader) and move it to the link connecting the
Emission node to the Material Output node to paste it in between them.
4.
Add a Geometry node (press
Shift
+
A
and navigate to Input | Geometry) and
connect its Backfacing output to the Fac input socket of the Mix Shader node.
5.
Switch the Emission node output from the first Shader input socket of the Mix
Shader node to the second node, as shown in the following screenshot:
Thanks to the Backfacing output of a Geometry node as Factor, a mesh-light can illuminate in only one direction
6. Save the file as
01_meshlight_final.blend
.
We have already seen that in a Mix Shader node, the first (upper) green Shader input socket
is considered equal to a
0
value, while the second socket is considered equal to a
1
value. So,
the Backfacing output of the Geometry node is telling Cycles to make the mesh-light plane
emit light only in the face-normal direction, and to keep the opposite back-facing side of the
plane black and non-emitting (just like a blank shader).
