User Guide > Lighting > Lights   

Area Lights

Houdini's two main light types both emit light from a single point which creates sharp shadows. To create softer shadowing, you can blur the shadows but this is not a realistic solution. Instead you can choose to set up and manage multiple light sources that are all slightly offset from each other. Area lights simplify this process by automatically distributing a number of light sources over a specified area. This will let you simulate the look of soft shadows that is generated by multiple light sources.

Topics covered:
Setting up an Area Light
Area Light Shapes
Using Different Light Types


Setting up an Area Light

To see the difference between the shadows cast by a single source light and an area light, you can use a scene that has a strong back light casting shadows into the foreground. The goal is to create shadows that are attenuated as you get further away from the columns.

You can use the following scene file to follow through the lesson steps.The scene consists of four columns sitting on a plane with a single point light behind the columns pointed in the general direction of the camera. The light is a point light with its Attenuation set to Physically Correct and its Dimmer value pumped up to about 33 to compensate.

Load Start File


Step One: Test Render the Point Light

RMB-click on the Render Launch button at the bottom of the viewer pane and select the mantra1 output to render. You can see the resulting sharp shadows being cast by the point light.

Step Two: Turn the Light into an Area Light

Select the light in the Network pane then in the Parameter pane, go to the Shading tab. Set Area Shape to Grid. Keep the Size to 1 and the Samples set to 16.

Re-render the image. Now the shadows are much softer with a clear attenuation as the shadow moves away from the column. The shadows render with a lot of noise which is a result of the low sample count used to render this light. The number of samples can be increased at the end after you are happy with the shape of the shadows. The light has been distributed over the surface area as 16 separate sources each with 1/16th of their original intensity.

Step Three: Set the Area Size

Next, set the Size to 3 while keeping the Samples set to 16. This increases the spread of the shadows and further softens the lighting effect.

Step Four: Set the Area Samples

Next set the samples to a higher value. This image used 2000 for maximum effect. Once the samples have been increased then then the rendered image appears more smooth. Obviously the longer render times produced by the higher sample rates must be balanced with the level of quality you require.



Area Light Shapes

There are five area light shapes to choose from. You can set their size to make them larger in the scene then transform the light itself to orient and position the light.

 

Line - With this shape, the lights will be distributed along the length of a straight line.
Grid - With this shape, the lights will be distributed over the area of a plane.
Circle - With this shape, the lights will be distributed over the area of a disk.
Sphere - With this shape the lights will be distributed along the outside surface of a sphere. You may want to put objects inside this shape for an overall soft shadow look that is similar to global illumination irradiance.
 

Tube - With this shape the lights will be distributed along the outside surface of a tube. You may want to put objects inside this shape for an overall soft shadow look that is similar to global illumination irradiance.

 


Using Different Light Types

You can choose to assign either point lights or spot lights to the area light shape. In both cases the light source will be distributed over the surface area of the chosen shape. In the case of spotlights, the direction of illumination will be determined by the look at and eye points of the light instead of the shapes normals.

Note: If you choose to use a spotlight with a small cone angle be aware that since the intensity of each light is divided by the number of samples your scene may appear dark because the light is not overlapping as much as it would with a point light.