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Question is how to create additive shader. If you need particles which just "add" light to a scene. Not render a surface but create emission.

If color changes from yellow to red for example, the red area of model does over-draw the yellow area (object behind) in case the emission does not understand to just add / increase color factor.

Non adaptive color in cycles

My project: Download Blend File (sorry, stackexchange responded with upload error)

How to math "add" color in cycles?

additive adaptive emission

Like Halo in Blender Render.

Blender Render

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  • $\begingroup$ Is your goal to light up some other object not shown in the image? Is your goal to create a glow? Or something else? Can you place an image in the question that shows your goal? Your second paragraph is difficult to read IMHO IIHO. $\endgroup$ – atomicbezierslinger Mar 29 '16 at 16:42
  • $\begingroup$ Goal is to have the image like in picture 2 (additive) and picture 3 (Add=1). $\endgroup$ – Nasenbaer Mar 29 '16 at 22:39
  • $\begingroup$ I'm thinking adding (not mixing) a transparent shader to the emission shader should do what you are after. I'll have to give it a try. $\endgroup$ – PGmath Mar 30 '16 at 1:40
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The way to do this is to add a transparent shader to the emission shader. This means that the surface will emit light and allow light to pass through it, so further emission materials behind it will add to the brightness.

enter image description here

Adding some randomized color produces this result. Note how the overlapping portions do indeed add up brightness as desired.

enter image description here

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  • $\begingroup$ Thanks! This is the best answer about additive blending I found. Where is the idea of "Add Shader" come from? How do you know that the RGB of "Emission" will be simply added to the ray trace's RGB value? Where did you learn these knowledge from? Official document doesn't have much detail. $\endgroup$ – cppBeginner May 18 at 5:16
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If what you're saying is true and you just want the particles to light the scene but not to be lit then you would simply use the is camera ray socket of the light path node to make the particle transparent for the camera while still contributing light to the scene. Another way of doing it would be to go to the cycles settings in the object tab of the properties pane and disabling ray visibility for the camera. However, in order for light to be visible, it has to be reflected off a surface. So if you only have particles in your scene that only add light but do not reflect light, then you'll end up with a black picture. Having said that, if you want your particles to render the light they emit but not to block off the light of other particles in the back, then I would suggest to use an add shader node to combine the emission shader with a translucent shader set to pure white. This way the material has both properties translucent and emit. enter image description here

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  • $\begingroup$ Thank you for the answer. But it does not look like expected. I uploaded the modified blender file. I also uploaded my original file in my question. When I add the add shader to it, it looks extreme red. If I remove the source color from refraction node, it looks white (without red). It is no RGB addition. goldengel.ch/temp/Writer_stackexchange2.zip $\endgroup$ – Nasenbaer Mar 29 '16 at 15:12
  • $\begingroup$ maybe if you use transparent instead of translucent (but keep the color white). I don't know the exact look you're after, but this should give you a basic idea of how you could approach it. $\endgroup$ – coCoKNIght Mar 29 '16 at 15:35
  • $\begingroup$ At the end I understand and you was already correct with your answer. I just did not understand the explanation. Now I do. Thank you. $\endgroup$ – Nasenbaer Mar 30 '16 at 10:01

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