# ImageBasedLighting

#### new Cesium.ImageBasedLighting()
engine/Source/Scene/ImageBasedLighting.js 27

Properties for managing image-based lighting on tilesets and models. Also manages the necessary resources and textures.

If specular environment maps are used, `ImageBasedLighting#destroy` must be called when the image-based lighting is no longer needed to clean up GPU resources properly. If a model or tileset creates an instance of ImageBasedLighting, it will handle this. Otherwise, the application is responsible for calling destroy().

Name | Type | Default | Description
--- | --- | --- | ---
`options.imageBasedLightingFactor` | Cartesian2 | `Cartesian2(1.0, 1.0)` | optional Scales diffuse and specular image-based lighting from the earth, sky, atmosphere and star skybox.
`options.luminanceAtZenith` | number | `0.2` | optional The sun's luminance at the zenith in kilo candela per meter squared to use for this model's procedural environment map.
`options.sphericalHarmonicCoefficients` | Array.<Cartesian3> |  | optional The third order spherical harmonic coefficients used for the diffuse color of image-based lighting.
`options.specularEnvironmentMaps` | string |  | optional A URL to a KTX2 file that contains a cube map of the specular lighting and the convoluted specular mipmaps.

### Members

#### imageBasedLightingFactor : Cartesian2
engine/Source/Scene/ImageBasedLighting.js 120

Cesium adds lighting from the earth, sky, atmosphere, and star skybox. This cartesian is used to scale the final diffuse and specular lighting contribution from those sources to the final color. A value of 0.0 will disable those light sources.

Default Value: `Cartesian2(1.0, 1.0)`

#### luminanceAtZenith : number
engine/Source/Scene/ImageBasedLighting.js 170

The sun's luminance at the zenith in kilo candela per meter squared to use for this model's procedural environment map. This is used when `ImageBasedLighting#specularEnvironmentMaps` and `ImageBasedLighting#sphericalHarmonicCoefficients` are not defined.

Default Value: `0.2`

#### specularEnvironmentMaps : string
engine/Source/Scene/ImageBasedLighting.js 223

A URL to a KTX2 file that contains a cube map of the specular lighting and the convoluted specular mipmaps.

##### Demo:

- Sandcastle Image Based Lighting Demo

##### See:

- ImageBasedLighting#sphericalHarmonicCoefficients

#### sphericalHarmonicCoefficients : Array.<Cartesian3>
engine/Source/Scene/ImageBasedLighting.js 198

The third order spherical harmonic coefficients used for the diffuse color of image-based lighting. When `undefined`, a diffuse irradiance computed from the atmosphere color is used.

There are nine `Cartesian3` coefficients. The order of the coefficients is: L0,0, L1,-1, L1,0, L1,1, L2,-2, L2,-1, L2,0, L2,1, L2,2

These values can be obtained by preprocessing the environment map using the `cmgen` tool of Google's Filament project. This will also generate a KTX file that can be supplied to `Model#specularEnvironmentMaps`.

##### Demo:

- Sandcastle Image Based Lighting Demo

##### See:

- An Efficient Representation for Irradiance Environment Maps

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