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There is already a post about it in here, but the problem is not solved, in fact it is not a solution to the problem. What can we do to avoid shadows from emission shaders?

There's a similar post about it in here, and still the problem is not solved, and it seems: LIGHT PATHS CANNOT BE USED FOR MESH LIGHTS.
Here is a blend file that contains a simple experiment that demonstrates that the aforementioned solution in the first link does not work:

So, how do we avoid mesh lights to cast shadows?

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  • $\begingroup$ Is this what you want? snapr.pw/i/4ce8554edd.png $\endgroup$ – Ezra Sep 8 '16 at 8:49
  • $\begingroup$ @Ezra, yes, how did you obtain it? $\endgroup$ – BumbleBee Sep 8 '16 at 11:11
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    $\begingroup$ I used the diffuse factor of a light path node to mix the diffuse shader of the cube with a transparent shader. Using the reflection output of the light path node gives the same result, so you might need to use both for more complex scenes. $\endgroup$ – Ezra Sep 8 '16 at 12:40
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    $\begingroup$ @Ezra, do you mean the 'Is Shadow Ray' factor of light path - it won't work with 'Is Diffuse Ray'. Also, this would have to be applied to all materials and would have the effect of removing shadows from all light sources rather than individually. One of the linked wuestions indicates disabling the shadows from all but one of the sources. $\endgroup$ – Rich Sedman Sep 8 '16 at 12:55
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    $\begingroup$ Try this: snapr.pw/i/1446ab92dd.png $\endgroup$ – Ezra Sep 8 '16 at 14:56
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In your particular example case you could replace your emitter object with an area lamp - this does support suppressing shadows as shown :

3d View : 3d View

Cast Shadow disabled : Without shadow

Cast Shadow enabled : With shadow

However, I don't think it's possible to suppress shadows from mesh-based emission materials due to the nature of the physics based rendering. ie, if you're suppressing light from emission surfaces then what about light reflected from a glossy surface - that could also cast shadows - as could light from a diffuse surface (albeit much more subtle, but it would still be a shadow).

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  • $\begingroup$ I deliberately was forming a simple scene here. To point out that the shadows do form $\endgroup$ – BumbleBee Sep 8 '16 at 11:09
  • $\begingroup$ Though, what you said is true $\endgroup$ – BumbleBee Sep 8 '16 at 11:10
  • $\begingroup$ I did think it was deliberately simplified. Do you have a specific practical situation in mind where the area lamp wouldn't be a suitable substitute? $\endgroup$ – Rich Sedman Sep 8 '16 at 13:54
  • $\begingroup$ I think emitters are particularly good for fill lights, but they cast shadows. Spots are better for casting sharp shadows. Emitters behave more like those metal sheets that emit in uni direction. $\endgroup$ – BumbleBee Sep 9 '16 at 1:42
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    $\begingroup$ The area lamp appears to produce pretty much identical results when compared to a rectangular mesh emitter - with the exception that the intensity for an area lamp is for the whole lamp whereas for an emitter it's per unit area (so double the size of emitter would produce an output 4 times stronger). The only reason I can see for using a mesh emitter is where the geometry of the emitter is significant - eg, modelling the filament of a light bulb - in which case you'd be looking for realism, including casting shadows. For general illumination, the area lamp is surely the better option. $\endgroup$ – Rich Sedman Sep 9 '16 at 7:39

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