How to? Single sided material with Cycles

Is this function currently not activated in Blender and Cycles?

I would like to turn my mesh lights into single surfaces instead
of emitting light into both directions.

With the Backfacing Geometry node you can do what you want, such as making the reversed faces invisible, or applying a different material to them.


or another trick here
you could add another plane behind your emission plane to stop it from spreading light on 2 sides!


That solution will work, but is not as efficient.

If you had a complex light source in mid-air for example, you would need to note that it’d be more difficult to change in the future and you’d still possibly have light leaking a little in the other direction at very steep angles.

Plus there is some evidence that the lightpath trick may actually create a very slight speed increase in some cases due to the reduction of uneccessary shading.

some leakage right

but you could make this extra plane a black hole node !
then nothing goes in or out and no leakage!


nice but this is not an emission plane !

it’s more like a composite shaders with one emission
but still a nice trick !


i think what your after is an area light… that will only emit in one direction and is a plane.

Unless I missed something, that type of light doesn’t create caustics like emission planes (that is according to the last time I tested them.)

As a result, I wouldn’t make a lot of use of them if you need truly realistic lighting.

Ok so I was right in the observation that there is no single sided option to turn on.

The node approach should work.