Volumetric Lighting in Vue 5
By jim coe April 15, 2006
For a complete discussion of light and color, refer to my $19.95 ebook, ‘Art Head Start’
This tutorial is available as a .pdf file
Intro
One of the most dramatic light effects is Volumetric Lighting (VL). In VL, the light cone from a light source is modeled as a more or less transparent object, considered as a kind of container of a ‘volume’. All materials inside the volume can have the full range of light interactions.
Without VL, light interactions are considered only at the surfaces of your objects, or more rarely, also at the surfaces of your light sources. The space between your light sources and objects is ignored.
VL allows you to render visible light cones because the volumetric light illuminates particles of haze, smoke or dust inside your light cone volume – just as in the real world.
Volumetric Lighting is lighting inside the light cone’s ‘Volume’.
Notice how the more distant blue sphere is partly hidden by the volume of illuminated particles.
You can even show colored shadows and the caustics projected by refraction from transparent objects inside your light beams. As usual, this includes control of refraction (light bending efficiency of a material) by setting your Index of Refraction (IOR).
Volumetric Lighting (VL) adds to the realism of your images, so they become more believable. More credible images let you to be more daring in your visual story telling, without leaving your audience behind.
VL includes full lighting control, including transparency parameters like Index of Refraction
Because VL readily evokes emotional responses in viewers, it is often used to simulate dramatic natural lighting.
And not only can it add drama, it can also with depth simulation by adding layers of visual depth and helping to differentiate your objects, as in the next scene.
The trick with VL is keeping settings low, so you can see inside and through your light beams
Tips and tricks
Your main precaution should be to go easy on both the light source intensity and Volumetric intensity, to avoid your light volume getting so bright it becomes opaque.
You don’t have to enable a Volumetric light type in the 'Atmosphere Editor > Light' tab to use VL. You can just enable it on a per-light basis, using the light source settings. In my test, changing to a Volumetric light type, without any other changes, didn’t increase render time.
For shadows to show in volumetric light cones, the brightness of other lights must be low. Typically, you’ll want to turn off the default sun and use a spotlight as your volumetric source. This means you may want to set some Atmosphere Editor > Light tab options to “Apply settings to all lights.”, although you don’t have to. All my examples were done with the Global Illumination (GI) light type. During setup and tweaking of VL, turn off all other light sources.
Start with a Volumetric intensity of 1.5, with the settings detailed below. Then slowly raise the intensity of the light source to a level somewhat below that which causes your light cone to go opaque – if you want to see through it or see shadows inside it.
You’ll also find it easier to see inside your light cone and maintain control, if the camera is more perpendicular to the cone than parallel to it. It’s especially tricky to get good VL effects if the camera is inside the light cone volume.
The ‘View through’ checkbox lets you look “down the barrel” of your spotlight for precise aiming. This is great when your spotlight cone is near the camera, or some other item you want it to miss.
Read the manual – there is a lot of vital info in there.
The manual seems to indicate that render times will be much longer with VL. I didn’t find that to be true for my (rather simple) scenes.
Light Sources
Usually, you will want a spot light for volumetric lighting, to give you the most control.
It’s possible to have multiple VL's, but a VL is so easy to wash out with other lights that I wouldn’t attempt multiple units until you are skilled in VL use.
Settings
Settings are located in these controls:
Light source controls:
• Lens Flare Editor
• Volumetric Light Options
• Shadow & Light Options
Be sure Shadows are set to 100% and “Use shadow map’ is enabled!
• The usual spot light controls, Color, Spread, Falloff, etc.
Atmosphere Editor Settings:
Since you don’t want ambient light washing out your VL effects, you may want to set the Ambient Vs Sun slider to 90% or 100% sun, then lower or zero the Skydome light gain and Artificial ambience. Global Illumination is heavily dependent on ambient light, so this is a trade-off that gives a less realistic GI render. You might even want to drop back to a Global Ambience (GA) render.
Volumetric Light Options:
The default settings of 1.000 for the scale of the illuminated particles in your volume give a look similar to clouds of smoke or dust, with clusters of particles in some areas, mixed with clearer areas. I usually want a much more even distribution of smaller clumps, so my typical scale is 0.01 or even 0.001.
I didn’t get much improvement during my experiments changing the ‘Smoke/Dust production’ function (in the Function Editor) or the Filter. But if you’re feeling adventurous, you should experiment in there.
Render Settings:
Here are my “User settings” type render settings.
My “User” render settings
Please remember that you don’t have to boost the volumetric render qualities until your final render – they can add a lot of render time.
Refraction Index
If you want to simulate how a certain material bends light and creates caustics, you can set a custom Index or Refraction (IOR) in the Material Editor’s Transparency tab. Note that you must also check the “Caustics” checkbox if you want to render caustics (the light patterns caused by refraction).
Below are some common IOR values and a link to a more complete list.
| Index of Refraction | ||
| Medium | Index | |
| Vacuum | 1.000 | |
| Air (Standard Temp & Pressure) | 1.00029 | |
| Water Ice | 1.31 | |
| Water (20° C, room temp) | 1.333 | |
| Crown Glass | 1.52 | |
| Flint Glass | 1.65 | |
| Glass Max | 1.9 | |
| Diamond | 2.419 | |
You can learn more at:
http://en.wikipedia.org/wiki/List_of_indices_of_refraction
You can set values of IOR not found in nature, but values much above that of diamond bend the light so much that little gets out to form a beam, so high values are not useful. Negative values will be rejected.
Light and color theory, including refraction, diffraction, caustics and many common light behaviors are thoroughly discussed in my $19.95 ‘Art Head Start’ ebook.
Cutting & Coloring Cones
In the Shadows & Light Options, the excellent Curves and Color Map options are underutilized. These let you attenuate the start or end (or both) of your light beam, as well as adding color blends to the light and setting an absolute cutoff distance.
Using these controls, you could, for example have a spacecraft laser weapon beam start smoothly some distance from the weapon, spread out at a controlled rate, change color along the beam and end smoothly at a controlled distance. Pretty advanced stuff!
Filter and Color Map settings
Filter and Color Map settings
That’s all for now. Hope it helped you!
Feel free to email me with any comments or questions:
_jim coe
