This page provides general information about the Fire Lights sub-section of the Rendering tab of the V-Ray Volumetric Grid.
The Fire Lights rollout controls how the fire casts light on the other scene objects as well as on the Volume Grid's own Smoke. When using Global Illumination (GI), the fire will illuminate everything automatically but the rendering will take quite long. Turning on Emit Light simulates GI by placing light sources in the bright parts of the fire, which gives similar results and renders much faster. The color and power of these lights are adjusted automatically but can be overridden. The smoke can be illuminated by the V-Ray Volume Grid's own fire with the Self Shadowing option. If enabled, the smoke will obstruct the path of light from the fire, creating a much more realistic look but decreasing rendering performance. To gain back the rendering speed, set Self Shadowing to Grid-based and use the Light Grid Resolution (%) parameter to reduce the resolution of the light grid.
All Fire Lights options are ignored when rendering with V-Ray GPU. Enable Global Illumination from the V-Ray Settings if you need the Smoke and/or the scene to be illuminated by the fire.
Create Fire Lights – When enabled, allows the fire to shine on smoke and on surrounding objects in the scene. See the Overview for more information.
If Create Fire Lights is enabled when rendering using GI, additional light sources will still be created by the fire at render time. You should disable Create Fire Lights if you want to let the GI naturally illuminate the scene.
Light Power on Scene | emLightsPowerMult – Controls the light intensity on all scene objects except the Volume Grid itself.
Light Power on Self | emLightsPowerOnSelfMult – Controls the power of the light on the Volume Grid's own smoke. This does not change the strength of the fire; only the illumination produced on the smoke is affected.
Self Shadowing | emLightsSelfShadow – Enables self-shadowing of the smoke from the fire's light. If this option is enabled, using smoke Scattering in the Smoke color rollout generally helps the light to illuminate a larger portion of the smoke, creating a more realistic self-illumination effect. See the Self-Shadowing example.
None – Smoke does not obstruct the light propagation and it is brightly lit.
Ray-traced – The same mechanism that illuminates the scene geometry is used on the smoke as well. This mode is physically correct and takes into account non-transparent obstacles inside the volume, but requires intense computation and can take considerable time to render. May produce noise in the rendered image.
Grid-based – The self-illumination of the smoke is calculated separately from the light that the Volume Grid casts on the scene using an approximate fast formula. While Ray-traced may produce noise, this mode has no such effect – the resulting illumination on the smoke is always smooth. However, any obstructing obstacles inside the volume are ignored by this mode. The Reduce grid to % parameter can be used to lower the resolution of the light grid and further speed up the illumination process. Reducing the grid generally produces smoother self-illumination.
Light Grid Resolution (%) | emLightsGrid – Specifies the resolution of the light grid as a percentage of the fire grid. Perfect illumination from the fire could be achieved by placing an Omni light in each fire cell, but this could take a tremendous amount of time to render and is usually not necessary to approximate the fire's illumination convincingly. For this reason, a separate light grid is created internally which can have a lower resolution than the fire grid, and this light grid is populated with an Omni light in each cell. The lower resolution (and thus fewer Omni lights) speeds up rendering at the expense of some illumination detail, which might not always be visible anyway. At a value of 100, the light grid has the same resolution as the fire grid. The more this value is decreased, the smoother the illumination becomes and the faster the rendering is. However, at very low values the fire might not blend well with the light it casts on the smoke. See the Grid Reduction example.
Decay Type | emLightsDecayType – Controls the speed with which the Volume Grid's emissive light fades as it propagates through space:
None – The light does not fade at all unless obstructed.
Inverse – The light intensity fades with the inverse of the distance. E.g. at a distance of 5 units, the intensity is 1/5th of the intensity of the emitter.
Inverse Square – The light fades with the inverse square of the traveled distance. This is physically correct light propagation. For example, at a distance of 5 units, the intensity is 1/25th of the intensity of the emitter.
Subdivs | emLightsSubdivs – Specifies the number of subdivisions to be used with V-Ray DMC Sampling. Higher values increase the quality, but slow down the render.
Caustic Subdivs | emLightsCaustSubdivs – Sampling control for Caustic effects. Similar to GI subdivisions, but used when caustics are calculated.
Emit Even If Not Renderable | emLightsPersist – When enabled, forces the Volume Grid to emit light even if the rendering is disabled. Can be used for compositing when the fire is rendered in a separate pass.
Self Shadowing = None
(render time = 2 min )
Self Shadowing = Ray-traced
(render time = 17 min )
Self Shadowing = Grid-based, Reduce grid to % = 10
(render time = 1 min )
Example: Grid Reduction
Self Shadowing = Grid-based, Light Grid Resolution (%) = 1
render time = 40 secs
Self Shadowing = Grid-based, Light Grid Resolution (%) = 10
render time = 58 secs
Self Shadowing = Grid-based,Light Grid Resolution (%) = 100 (no reduction at all)
render time = 6:39 mins