A quick guide with an example of how to define geometry as a light in SideFX Houdini.
Create a geometry in a scene, in this case, I’ve added a torus object to an existing test scene:
![](https://i2.wp.com/www.john-player.com/wp-content/uploads/2019/06/houdini-geometry-light-1.png?fit=800%2C434)
Double click the torus node to expand and adjust its properties to suit:
![](https://i0.wp.com/www.john-player.com/wp-content/uploads/2019/06/houdini-geometry-light-2.png?fit=800%2C507)
Once you are happy with the torus properties, return to the global network, select the torus geometry and click “Geometry Light” in the ‘Lights and Cameras’ shelf:
![](https://i2.wp.com/www.john-player.com/wp-content/uploads/2019/06/houdini-geometry-light-3.png?fit=800%2C503)
A new light node will be created in the network, you can adjust its properties to define the light attributes:
![](https://i0.wp.com/www.john-player.com/wp-content/uploads/2019/06/houdini-geometry-light-4.png?fit=800%2C529)
To see the light geometry in the render, enable the ‘Render Light Geometry’ option:
![](https://i0.wp.com/www.john-player.com/wp-content/uploads/2019/06/houdini-geometry-light-5.png?fit=800%2C401)