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Environment lights illuminate the scene from a virtual hemisphere (or sphere) that is beyond that farthest geometry objects in the scene. Environment lights can be rotated to orient directional illumination, but they cannot be translated.
An environment light may use a texture map to provide HDRI illumination from an environment map. With no rotation, the environment map is oriented so that the top face aligns with the positive Y axis.
See how to create an environment/reflection map.
Parameters
Transform
Transform Order
The left menu chooses the order in which transforms are applied (for example, scale, then rotate, then translate). This can change the position and orientation of the object, in the same way that going a block and turning east takes you to a different place than turning east and then going a block.
The right menu chooses the order in which to rotate around the X, Y, and Z axes. Certain orders can make character joint transforms easier to use, depending on the character.
Rotate
Degrees rotation about XYZ axes.
Viewing Options
Display
Whether or not this object is displayed in the viewport and rendered. Turn on the checkbox to have Houdini use this parameter, then set the value to 0 to hide the object in the viewport and not render it, or 1 to show and render the object. If the checkbox is off, Houdini ignores the value.
Icon scale
Scales the viewport geometry. This parameter is only for display purposes.
Cache Object Transform
Caches object transforms once Houdini calculates them. This is
especially useful for objects whose world space position is
expensive to calculate (such as 
Sticky objects),
and objects at the end of long parenting chains (such as
Bones). This option is turned on by default for Sticky and
Bone objects.
See the OBJ Caching section of the Houdini Preferences window for how to control the size of the object transform cache.
Viewport Selecting Enabled
Object is capable of being picked in the viewport.
Select Script
Script to run when the object is picked in the viewport. See select scripts .
Lookat Options
Light
Light Color
The environment color or environment map tint if a map is used.
Light Intensity
A scale on the color. If the intensity is 0, the light is disabled. The light will only be sent to the renderer if the object is included in the Force Lights parameter of the output driver.
Environment Map
Environment map to control the color and intensity of light arriving from different directions. The color from the environment map will be tinted by the light color.
This parameter will be disabled if Enable Sky Environment Map (on the Sky Environment Map tab) is on.
Light Enabled
Turning this toggle off is equivalent to setting the light intensity to 0.
Enable Light In Viewport
Turning this off removes the light from consideration in the viewport. This is useful for lights which only make sense at render time.
Diffuse contribution
The light will contribute to diffuse illumination when illuminating a surface.
Specular contribution
The light will provide specular highlights on the surface when illuminating a surface.
Light Contributions
Provides more detailed control over which shading components the light affects. To disable contribution to a named comopnent, specify the component name and disable the toggle.
Render Light Geometry
Display the light as a geometry object in the render. Environment lights will appear as a background image in the render when this toggle is enabled.
Clip To Positive Y Hemisphere
Forces the environment lighting to only emit light from the +Y hemisphere. When lighting a scene that occludes most illumination in the -Y hemisphere (eg. a scene with a large ground plane), turning on this toggle can improve rendering quality.
Categories
The space or comma separated list of categories to which this object belongs.
Currently not supported for per-primitive material assignment (material SOP).
Render Options
Options that affect how light is produced by the environment light.
Rendering Mode
The sampling style for environment illumination. Environment lighting is computed with raytracing by sending rays out into the hemisphere above the shaded surface to analyze the amount of light arriving at the surface from different directions.
Which rendering mode you choose to use will depend on the type of environment illumination as well as the geometry in your scene.
Direct Lighting
The environment will be treated as a large area light enclosing the scene. If an environment map is used, mantra will send more samples toward bright portions of the environment. If you want the environment to contribute to specular or reflective surfaces, you should use this option.
Direct lighting enables support for variance antialiasing when rendering with PBR or when using the /nodes/vop/surfacemodel VOP. Variance antialiasing makes use of the min/max ray samples to automatically detect and reduce noise in the lighting.
Tip
Normally "Direct Lighting" should be preferred in the following scenarios:
-
When the environment map contains directional illumination (eg. parts of the map are much brighter than others)
-
When you require a specular contribution from the environment
-
When you require per-light exports
Ambient Occlusion
The environment will be computed using ambient occlusion. Ambient
occlusion is computed using the 
VEX Global
Illumination shader, and will send evenly
distributed rays in the hemisphere to check for blocking surfaces.
Ambient occlusion works best when computing lighting without an
environment map or with a map that has little variation in color
over the hemisphere. Occlusion will only contribute to diffuse
lighting.
Tip
Use ambient occlusion in the following scenarios:
-
When rendering without an environment map or when the environment lighting is uniform and not very intense.
-
When using irradiance caching.
Ray Tracing Background
The environment will contribute to the scene indirectly for shaders that trace rays that exit the scene. This mode is supported through the resolvemissedray VEX function, which can be used in shaders to query the background illumination for a given ray. Ray Tracing Background mode is supported for the following scenarios:
-
PBR rendering (either micropolygon or raytracing)
-
Non-PBR rendering when using the /nodes/vop/surfacemodel VOP
In this mode, deep rasters from the environment light will appear in the "indirect_emission" export plane rather than the per-light diffuse/reflect/refract planes. This will occur because the light is treated like an emissive background object rather than as a true light source.
Tip
Normally "Ray Tracing Background" should be preferred in the following scenarios:
-
When rendering without an environment map or when the environment lighting is uniform and not very intense
-
When you are using PBR or a shader that performs ray tracing to calculate most indirect lighting
-
When using an
Indirect Light to calculate irradiance, to speed up lighting for secondary rays
Sampling Quality
The sampling quality multiplier for the light. A value of 1 will use the ray sampling parameters (Min Ray Samples) from the output driver directly. Other values will proportionally increase or decrease the sampling quality.
Glossy Filter Amount
When set to a non-zero value, this parameter enables renderer-controlled filtering of the environment map to filter out high frequency noise in glossy reflections of the environment light. The amount of filtering is determined by the surface bsdf - with glossy surfaces receiving more filtering. Filtering is automatically disabled for diffuse surfaces and for mirror reflections to preserve accuracy in the render for these components. Using a non-zero value for this setting may change the average brightness of the glossy highlights, introducing some bias in the render.
Portal Geometry
Specifies a geometry object that can be used to optimize sampling of environment lights in enclosed scenes. The portal geometry describes to the renderer where light can enter the enclosed scene, so that the sampling algorithm can concentrate on the parts of the environment that actually contribute lighting to a pixel. Normally, the portal geometry should be a geometry object that is not rendered, so that it does not cast shadows on the scene, and that has only a single layer of surface visible from any point in the scene - so that illumination is not multiply counted.
A correctly configured portal should produce the same rendered result as when the portal is disabled, but with much less noise. Portals should normally not be used in outdoor scenes where the environment map is fully visible, or when the environment map contains sharp variations in intensity - since in these cases the standard direct lighting algorithm may produce better results.
Using an environment light with a portal is equivalent to creating a
standard 
geometry light with physically correct
attenuation, no intensity normalization, and transform into this object
enabled.
Ray Distance
Maximum distance from the sample point to consider geometry for irradiance/occlusion.
Sampling Angle
Half-angle over which to send rays for irradiance/occlusion. 90 degrees is a full hemisphere.
Adaptive Sampling
Turns on an automatic optimization that will reduce the number of samples when there is little variation in occlusion above the sample point. This can improve performance at the expense of some possible flickering or additional noise. Adaptive sampling will only take effect with more than 64 samples.
Sky Environment Map
Options to automatically create a "sky and ground" environment map for the light.
Enable Sky Environment Map
Automatically create a "sky and ground" environment map. When this parameter is on, the Environment Map parameter (on the Environment tab) will be disabled.
Resolution
The resolution (in pixels per cube side) of the environment map.
The other parameters on this tab are identical to the parameters of
the 
Sky Environment Map compositing node.
Direction
The type of direction to calculate. Either Away from Sun or Towards the Sun.
Calculated Vector
The direction vector for the sun.
Calculated Rotate
The Euler rotation angles to align -Z axis with the Calculated Vector.
Shadow
Shadow Type
None
No shadows will be cast by this light.
Ray-Traced Shadows
Ray-tracing will be used to compute shadows from this light source.
Shadow Mask
A mask of objects which will be considered occluders for the light source. When ray-traced shadows are used, only these objects will be intersected by shadow rays. When depth map shadows are used, only these objects will appear in the depth map.
Note
It is possible to use categories by adding the shadowcategories rendering parameter.
Shadow Intensity
A scale on how much light is blocked by occluders. By decreasing the shadow intensity, the occluders will not block all the light, allowing some illumination through.
Transparent Shadows
When this option is turned on, the surface shader of occluders will be evaluated to determine the opacity. Turning this option on will cause deep shadow maps to be used when shadowing using Depth Map Shadows.
Examples
PortalBox Example for Environment Light object node
This example shows how to create a portal light using window geometry. A box is modeled and then split into 2 SOPs - one representing windows and the other walls. The walls are rendered, while the windows are used to specify the portal for an environment light. Toggle on and off the portal to see the render quality difference while rendering in the Render View.
The following examples include this node.
ClipLayerTrigger Example for Agent Clip Layer dynamics node
CrowdHeightField Example for Crowd Solver dynamics node
PartialRagdolls Example for Crowd Solver dynamics node
Formation Crowd Example Example for Crowd Solver dynamics node
Stadium Crowd Example Example for Crowd Solver dynamics node
Street Crowd Example Example for Crowd Solver dynamics node
PortalBox Example for Environment Light object node
TubeCaustic Example for Indirect Light object node
AmbientOcclusion Example for Mantra render node
