Lights - Arnold for Houdini
Further Reading |
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See also Lights in the Arnold User Guide |
To add any lights to a scene an Arnold Light needs to be created. This node is used for all lights in Arnold for Houdini. It can be used as a point_light, distant_light, spot_light, disk_light, cylinder_light, quad_light, mesh_light, skydome_light, or photometric_light.
An Arnold Light node can be created by tab-typing Arnold Light in the Network Editor at object level (Tab > Arnold > Arnold Light).
- The half distance attenuation that is available on Houdini lights is not supported in Arnold. To tweak the attenuation use the Light Decay filter.
- Volume_samples do not apply to the atmosphere_volume atmosphere shader in the Environment section. To improve the quality of the atmosphere_volume atmosphere shader, you must increase the Atmospheric Scattering samples.
- Information about creating per-light AOVs can be found here.
- The native Houdini lights won't be translated. Arnold lights must be used.
- Although the light will not contribute to the render, it will still be visible in the viewport.
Light instancing
You can instance and render Light SOPs. Solaris lights, or lights created by a procedural, are not supported yet.
![](https://help.autodesk.com/cloudhelp/ENU/AR-Houdini/images/htoa_light_instances.png)
Common Parameters
These properties are available to all types of Arnold Lights.
Color Type
Choose between Simple Color, Texture, or Shader.
Shadows
These settings are common to all lights.
Contribution
These settings are common to all lights.
Viewport
Turns on/off the preview of the effect of the light in the Houdini viewport.
The Arnold Light works with Houdini's high-quality viewport display. To enable it, click on the High-Quality Lighting Icon in the right-hand viewport bar. The preview is created using Houdini point lights and therefore some Arnold Light parameters will have no preview, such as radius affecting shadow softness. Mesh lights cannot be previewed.
- Although the light will not be visible in the viewport, it will still contribute to the render.
- Currently, it is not stable to enable shadows viewport preview. Doing so may crash Houdini.
Cylinder Light
The cylinder light shape simulates light from a cylindrical area source (tube shape). Increasing the size of the cylinder light will create a larger area light size and therefore will soften the shadows that run perpendicular to the cylinder’s axis. Cylinder lights will always be circular. It is not possible to scale the width to create an ellipse.
Disk Light
The disk light shape simulates light from a circular area source (flat disk).
Distant Light
This is a parallel light from a distant source, specified in terms of a direction vector. Often used to model sunlight.
Light Portal
Skydome lights can use light portals to reduce noise for interior scenes, where the light comes in through relatively small openings. Instead of emitting light, they can be used to guide skydome light sampling. Light portals must be placed to cover all windows, doors, and other openings through which skydome light comes into the scene.
The light portal should be oriented so that it is pointing in through the window as indicated below:
Light portal pointing inwards outside window
Mesh Light
In situations where conventional light shapes will not suffice, mesh lights are more suitable. Mesh lights can be used to create interesting lighting effects that would not be possible any other way. For example, effects such as neon lighting or a car light motion trail effect can be achieved more easily with mesh lights.
Quad Light
Simulates light from an area source (a quadrilateral, specified by four vertices). It can be used to model light from an extended source (fluorescent strip lights) or in some circumstances from a window.
Photometric Light
Photometric lights use data measured from real-world lights, often directly from bulb and enclosure manufacturers themselves. You can import IES profiles from companies such as Erco, Lamp, Osram, and Philips; their IES files provide accurate intensity and spread data for a given light model.
Point Light
Although named point for historical reasons, this light source can model light either from a (theoretical) point source, or from a sphere (the latter being more realistic in most cases, and producing less sharp shadows). The light is cast evenly in all directions.
Spot Light
This simulates light from a spotlight, as a cone of light from the position of the light toward the point it is pointed at.
Skydome Light
This simulates light from a sphere or dome above the scene, representing the sky. It can also be used with high dynamic range (HDR) images to perform image-based environment lighting. This is the node that is typically used for lighting exterior scenes. The skydome_light has a texturable color slot so that you can map a texture to be used for IBL.
Filters
Arnold light filters are arbitrary shaders that can modify a light's output based on distance, position or other factors. This makes it easy to extend the built-in light sources with additional effects.
Light Filters are created within Arnold Shader Networks and must be connected to a light filter output node. You can connect several filters. The vopnet is then connected to Arnold Lights under the Light Filter tab. For convenience, a default shader network containing a light filter output is created within the light node.
Arnold "light filters" are arbitrary shaders that can modify a light's output based on distance, position, or other factors. This makes it easy to extend the built-in light sources with additional effects.
Attaching Light Filters To Lights
Light filters are created within Arnold Shader Networks and must be connected to a light output node. The vopnet is then connected to Arnold Lights under the Light Filter tab.
By default, when you click on the filters tab of a light, a vopnet will be created already within the light. Clicking the 'Jump To' arrow will take you inside obj > arnold_light1 > shopnet > arnold_vopnet. This is created here for convenience. However, an Arnold Shader Network vopnet could be created in the SHOP and linked to the light using the operator chooser.
When choosing the operator from the shop either the vopnet or the output node can be selected. If the vopnet is chosen and it contains multiple Output nodes then Arnold will use the first one it finds.
Creating Light Filters
In your chosen vopnet Tab-type (Custom > Light Decay / Light Blocker / Gobo / Barndoor ) to create a light filter node. Connect the output of the light filter node to the Light Filter # parameter of the light output node. As one is connected another empty input will be added. It is not possible to use more than one gobo or barndoor filter on the same light.
Barndoors
Barndoors are opaque moving panels attached to the sides of the light's opening used for additional control over the shape of the light beam.
Gobo
The gobo filter is used to break up the light beam into an irregular, more natural pattern such as tree leaves, etc.
Light Blocker
The light_blocker filter will block out an arbitrary geometrically defined area of a connected light.
Light Decay
The light_decay filter specifies the attenuation ranges of where the light starts and ends.