Irradiance as the source of light

You can render a scene with Final Gather without a single light source. In this case, the scene is illuminated by the scene irradiance or total incoming irradiance instead of surrounding surfaces. You can provide irradiance information by:

• Adjusting the material’s Ambient Color attribute (found in the Common Material Attributes section of that material’s Attribute Editor).
• Adjusting the material’s Incandescence attribute (found in the Common Material Attributes section of that material’s Attribute Editor).
• Mapping a file texture to the material’s Irradiance attribute (found in the mental ray section of that material’s Attribute Editor). For example, you could import an image or series of images (to use as file textures) that mimic the emerging light at early dawn, before the sun (direct light source) has risen.

  The Irradiance Color attribute lets you control the effect of color bleeding.