The available world light types are:
- Sky: A physically correct sky (Hosek and Wilkie sky model). Can be used alone or with a sun light.
- HDRI: Lights the scene with a high-dynamic range image (latlong mapping).
- Flat Color: Lights the scene with a solid background color.
- None: No world light. Use for completely enclosed interior rooms.
Sun: If you use a sunlight in the scene, you should select it in the sky settings. The sky will then derive its color from the sun position (it gets more reddish when the sun is close to the horizon). It will also copy the gain (brightness) and turbidity (fogginess) settings from the sun lamp.
Image: Usually you want to use a HDR image here (extension ".hdr" or ".exr"). Some places where you can get them are linked here. You can also use normal LDR (low-dynamic range) images (".jpg", ".png" etc.) but they will light your scene very uniformly and won't create strong shadows and highlights.
The image should use the latlong mapping (latitude-longitude). For an example see the image below. (It is the same mapping produced by LuxCoreRender's panoramic camera)
Gamma: Should be set to the gamma of the image. HDR images are usually saved with gamma 1.0, while most LDR images are usually saved with gamma 2.2.
Z-Axis Rotation: Can be used to rotate the image around the Z-Axis. If you want to rotate the image around other axis, use a hemi lamp instead of the world light and set the world light to None.
Sample Upper Hemisphere Only: Enable this option if you are using a ground with shadow catcher material in the scene. This option will prevent shadows being cast from below, which would lead to incorrect shadow catcher appearance.
Importance: How much processing power to spend on this light source compared to other light sources. Used to scale the light importance computed by the light strategy. For instance, if you set a uniform light strategy, a light with a user importance of 2.0 will be sampled 2 times more often than one with 1.0. If you use a power light strategy, the user importance will be multiplied by the light power.
When you manually set the importance, you usually also want to set the light strategy to uniform (so you have full control on how the lights are sampled).
Build Visibility Map: If enabled, the visibility map for the world light source is computed at the start of a final render (not in viewport).
Here you can enable/disable the visibility of the world background to the three light bounce types. This setting is not supported by the Bidir engine as of v2.0alpha7.
- Diffuse rays include for example the matte material, the matte base of the glossy material, the matte translucent material etc.
- Glossy rays include any "non-sharp" specular reflections/transmissions with a roughness setting, e.g. glossy coating, metal, rough glass etc.
- Specular rays include any "sharp" specular reflection/transmission without a roughness setting (glass and mirror materials)