Sky Light

To lighten outdoor scenes you often just want to illuminate the scene by the sun and the sky. You might now think what is the difference between the sun and the sky. Doesn't all the light come from the sun? And yes, you are right. But in the context of the sky light object the sun light is considered as two parts.

  • The light coming straight from the sun without scattering. This part of the light is approximated by a distant light.
  • The sky light is light which has been scattered by the atmosphere. It can be considered as a huge hemispherical area light.

When illuminating a scene with a sky light the light source will always use it's first sample for the direct sun light. All other samples will be used to approximate the sky illumination.

Attention: You can have multiple Sky and HDRI Lights in your scene but Cheetah3D will just use the first one for rendering.

Properties

  • Intensity: The intensity of the sky light. The intensity normally doesn't have to be changed.
  • Turbidity: Sets the turbidity of the atmosphere. This value should be between 2-10.
  • Albedo: This property sets the diffuse reflectivity of the ground surface.
  • Samples: Number of samples at which the sky light will be evaluated. The more samples you use the smoother the shadows will become. The rendering time will increase substantially with more samples. For a pure skylight 16-32 light samples should be fine.
  • MIS: Turns on MIS (Multiple Importance Sampling). MIS considerably improves the convergence speed of the renderer. So less samples are need to get the same quality. MIS only works with the Falcon renderer.
  • Background: Turn this property on if you want to use the skylight as a background.
  • Latitude: Since the position of the sun depends on your position on the earth you have to tell Cheetah3D where the scene should be located on the earth. Sets the latitudal position of the scene [-180°, 180°]
  • Longitude: Sets the longitudal position of the scene [-180°, 180°]
  • Date: Time and date. This determines the current position of the sun at the sky. The date is set in the following format "hh:mm MM/YY"
  • Shadow type: Use this property to choose the shadow calculation type. See the description of the various modes in the Light object.
  • Shadow color: The color of the shadow.