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How can I make a cycles material that gets very bright when a light is shown on it, yet still has normal colors?
I'm talking about the "Retroreflective sheeting" that can be seen on road signs, the tape on big trucks (like in the image below), traffic barricades and clothing.
truck with reflective tape on the side
Image by TollGroup on wikimedia commons

This reflective stuff has a interesting property where the colors show up perfectly well, but when exposed to a light source they seem to reflect much more light the normal. This site has lots of good reference images.

I have tried different combinations of glossy and diffuse shaders, but none work as I have yet to get the super bright reflections.

How can cycles make a material that reflects so much light, and keeps the colors correct?

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  • $\begingroup$ The angle of reflection should be directed back to the source of light at each point where the light hits the surface. $\endgroup$
    – Denis
    Commented Dec 21, 2016 at 6:11
  • $\begingroup$ I'm not at my computer, but I had a thought. If you have the time to experiment, try this: duplicate the mesh that you desire to have reflect like this and move it ever so slightly in front of the original. Treat the original as your color backdrop, and for the duplicate, subdivide the heck out of it, and parent a grain sized cycles glass material low poly icosphere to its origin, then for duplication, set it to verts (subdivide until it looks like you took a handful of glass sand and threw it at wet paint). In reality this will give that kind of reflective property. $\endgroup$
    – Rick Riggs
    Commented Dec 21, 2016 at 7:05

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Such a material works by reflecting the incoming light back towards the direction it originated - since your car headlights are very close to your own line of sight, you see a strong reflection of your own lights. You can replicate this behaviour in a material by simply manipulating the surface Normal in a Glossy shader that can then be mixed into any other shaders on the material - as shown :

reflective material

The key here is to connect the Geometry Incoming socket to the Normal of the Glossy shader so that any reflections occur back towards the source. You can manipulate the Roughness to control how sharp the reflection is (ie, roughness of zero would reflect all light direct back to the source but a slight roughness will spread it out, to allow it to be visible (but fainter) at wider viewing angles) - and so how close to the light souce line of sight the viewer must be to allow them to see its reflection.

Any light source close to the line of sight of the camera will now strongly reflect back and make the material appear to 'glow' with respect to other (non-reflective) materials. You can vary the Color of the Glossy node to affect the color of the reflection.

Example showing one reflective cube and one 'normal' cube :

cats eye material

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    $\begingroup$ I wish I could +10. This adaptive normal technique is smart af! $\endgroup$
    – Sibbs Gambling
    Commented Aug 9, 2017 at 2:18

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