This page provides general information about the Fire Lights sub-section of the Rendering rollout of Phoenix FD.

Overview

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The Fire Lights rollout controls how the fire casts light on the other scene objects as well as on the Phoenix FD Simulator's own Smoke. When using Global Illumination (GI), the fire will illuminate everything automatically but the rendering will take longer. Turning on Create Fire Lights 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 illumination caused by the Simulator's own fire can be controlled 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.

Parameters

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Create Fire Lights | emLightsCountEnbl – When enabled, allows the fire to shine on smoke and on surrounding objects in the scene. See the Overview for more information.

Light Power on Scene | emLightsPowerMult – Controls the light intensity on all scene objects except the Phoenix FD Simulator itself.

Light Power on Self | emLightsPowerOnSelfMult – Controls the power of the light on the Simulator's own smoke. This will not change the intensity 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 lights. If this option is enabled, using smoke Scattering in the Smoke color rollout will generally help the light to illuminate a larger portion of the smoke, creating a more realistic self-illumination effect. See the Self-Shadowing example.

None – Smoke will not obstruct the light propagation and will be brightly lit.
Ray-traced – The same mechanism that illuminates the scene geometry will be 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 will be calculated separately from the light that the Phoenix FD Simulator casts on the scene using an approximation 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 will generally produce 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 will become and the faster the rendering will be. 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 Simulator'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 will be 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 will be 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 will increase the quality but will slow down the render.

Caustic Subdivs | emLightsCaustSubdivs – Sampling control for Caustic effects. Similar to GI subdivisions, but used when caustics are calculated.

Create Lights Even If Not Renderable | emLightsPersist – When enabled, forces the Simulator to emit light even if the rendering is disabled. Can be used for compositing when the fire is rendered in a separate pass.

Example: Self-Shadowing

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Example: Grid Reduction

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