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 even without using Global Illumination (GI). With GI, the fire will automatically illuminate the other scene objects and the simulator's own smoke, but the rendering will take quite long. Enabling Create Fire Lights simulates GI by placing light sources in the bright parts of the fire, which produces similar results and renders much faster. 

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 light. 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. See the Self-Shadowing example.

None – Smoke will not obstruct the light propagation and will be brightly lit.
Ray-traced – The simulator's smoke will be illuminated by the fire's light sources using precise but slow ray-tracing. Note that the fire lights always illuminate the rest of the scene using ray-tracing. This mode is physically correct and takes into account non-transparent obstacles inside the Phoenix volume, but requires intense computation and can take considerable time to render and clear the noise from the image.
Grid-based – The self-illumination of the smoke will be calculated separately from the light that the simulator 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 obstacles inside the Phoenix volume are ignored by this mode and will not cast shadows on the smoke from the simulator's own light. The Light Grid Resolution (%) 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. Note that using Grid-based self-shadowing requires additional memory, so beware of high RAM usage with high resolution grids or many copied or instanced volumes.

Light Grid Resolution (%) | emLightsGrid – Specifies the resolution of the light grid as a percentage of the fire grid's resolution. Perfect illumination from fire could be achieved by placing a light in each fire cell, but this could take a tremendous amount of time to render and such accuracy is usually not necessary. In order to speed up rendering, a separate light grid is created internally which can have a lower resolution than the fire grid, and this light grid is populated with one sphere light per each cell. The lower resolution (and thus fewer 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 smaller the Light Resolution is, 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 how quickly the simulator's emissive light fades when travelling away from the fire light sources:

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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