You can now use custom ICE attributes with the Map Lookup and Attribute shaders. This is very useful for procedural modeling, because you do not need to create clusters in advance for all the attributes that you want to use in your render trees.
If this option is on, the shader is added as a lens shader on the pass when you run the plug-in. This shader gives the correct candela-per-meter scale factor so that the image doesn't look overexposed (it tones the brightness down). You can adjust the brightness of the image using the Shutter Time and the F-Stop values in the lens shader.
If this option is off, the Photographic Exposure (mia) shader is not added, so you have more control over the brightness values using the Physical Sky shader parameters, or using a different lens shader. As well, these Physical Sky shader parameter values are automatically set: Multiplier: 0.01; RGB Unit Conversion: 0.001 for all channels.