How can a light cone (volumetric) be setup with cycles?

Question

I tried to reproduce the results from the Docs on volumetric lighting unfortunately the video link is broken. And I might have overlooked some related settings.

The spot light is barley visible on the ground.

Increasing the Density of the Volume Scatter Node darkens the sky texture but leads to some light cone from the car's headlight. (only 10 samples in preview).

Which settings do I need to change or should I try a different approach?

Integrator settings are default and spotlight settings were copied from the example found in the docs.

Related:

• Creating volumetric lighting (crepuscular rays) in Cycles (pre 2.7)

• How do I properly set up a spotlight cone? (BI only)

Answer 1

In real life these effects are caused by particles in the air such as water droplets, which reflect and scatter light. Usually these effects are only clearly visible when there is not a lot of other light sources, such as at night.

In your case it looks like you are going for a more non-photorealistic look, so you may want to give up on trying to simulate the scattering and just use an emission shader.

1. Add some cones to act as the light sources.
   Note that they shouldn't intersect or contain non-manifold goemtry. If you want to intersect them, use a boolean modifier or a remesh modifier to make the final geometry intersection free.

   

2. Add some nodes with a horizontal gradient to fade the intensity of the emitted light out before the hard edge at the end of the cone. Note that this particular mapping setup assumes that the origin of the cone is at the point, and that the rotation is not applied.

   

   In this example I also made it so the cone material doesn't illuminate other objects, as I wanted to do the illumination only with spot lamps to further reduce noise. The last mix shader is optional.

There are some limitations, for instance there are no volumetric shadows. But not too bad for converging in about 20 samples :)

Answer 2

Seeing a cone of light requires a bit of playing around with a couple of variables. Once you add volume scattering in your world, the lights in the scene get dimmer, as they have to travel through the "foggy atmosphere". You'll have to increase the values for the lights quite a lot. The brightness will then depend on the density of the volume scattering, the intensity of the light, and the distance of the objects to the camera.

One thing to remember is that the lights will be more noticeable against a dark background.

For a cleaner render increase the number of samples for volume (set by default to 0) in the light paths tab, and increase also the number of overall samples for the render (and expect much, much longer rendering times)

EDIT: Just to illustrate how changing the camera distance affects things.

Once the camera was moved further away, I had to change the density to a lower value and increase the value in the lamp's brightness to keep things visible.

Answer 3

Even though this question was asked some time ago, I feel like I need to share a way I have found that simplifies this process a ton and gets the effect I feel you want.

I first created a spot lamp (in place of your headlights) and created a cube (but you can use any solid mesh). I scaled the cube way up so that it covered up most of the spot lamp. Then I scaled the top and bottom so that it fit the cone of light better.

Then I created a new 'page' and made it a node editor. I then gave the cube a new material and clicked the "use nodes" button.

Next I deleted the Diffuse Shader so that just the Material Output node remained.

Finally, you add a Volume Scatter node by pressing Shift+A and searching for "volume scatter". Once that is in, connect the Volume output on the Volume Scatter node to the Volume input on the Material Output node.

And you're done! You can play with the density to your liking. I usually bring it down from 1 to .3 or lower.

This is a pretty big setup so I brought the brightness of the spot lamp to 200. Unless your cars are absolutely massive, this should be more than enough to give that light cone effect. The light near the top of the render is the spot lamp.

These are the settings that I would have if I were doing what you are/were doing: density at .08 and shape the cone around where the light actually shines so that you don't get that foggy look.

Congrats, you've just created a light cone in Cycles Render!