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One of the most dramatic 3D scene lighting 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 for a volume of materials. All materials inside this 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, and control their look, because the volumetric light simulates the illumination of particles of haze, smoke or dust inside your light cone volume – the sort of illumination of fine particles which makes light beams visible in the real world.
VL settings let you render the volume's particles individually as coarse “grains", or the whole light cone can be somewhat opaque to simulate very fine 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 at the surfaces of a material) by setting your Index of Refraction (IOR).
Volumetric Lighting adds to the realism and drama of your images, so they become more believable and compelling. More credible images let you to be more daring in your visual story telling, without leaving your audience behind.
Because VL readily evokes an emotional response in viewers, it’s often used to simulate dramatic natural lighting.
And not only can it add drama, it can also help with depth simulation by adding layers of visual information and by helping to differentiate your objects, as in the scene below.
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 one VL light source at a time.
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 to 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 (maybe impossible) 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 a volumetric spotlight, for precise aiming. This is great when your spotlight cone is near the camera, or some other item you need it to miss.
Also be sure to 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.
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.
Light source controls:
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.
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.
Here are my “User settings” type 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.
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|
|Air (Standard Temp & Pressure)||1.00029|
|Water (20° C, room temp)||1.333|
You can learn more at:
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.
In the Shadows & Light Options, the excellent Curves and Color Map options are underutilized by many 3D artists. 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!
Of course you'll often want to attenuate the start of your light beam, to make it the size of your visible light source. For example, you don't want the beam of a searchlight to start as a sharp point, but as the same width as the searchlight's opening.
In another tutorial, you can see how that light attenuation curve can be used with notched cut out of it to actually attenuate the light falling on surfaces at a certain distance from your light source - while still illuminating more distant surfaces!
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For more on 3D scene lighting, please see: Complex 3D Scene LightingWishing you a creative future!