mental ray attributes are available only for point, spot, directional and area lights. Find these attributes on the LightShape node in the Attribute Editor.
mental ray area lights can be created using spot lights or area lights. For more information on mental ray area light attributes, see mental ray Area Light Attributes (created using area light) and mental ray Area Light Attributes (created using spot light).
Caustic and Global Illumination
The amount of light distributed by the light source. Each photon carries a fraction of the light source energy.
8000 is the default. 0 means no photons are emitted.
If caustic effects are not bright enough, try increasing these values equally, in small increments (to 12000, to start) until you have better results.
If ‘hot spots’ (blown out) areas occur, try decreasing these values equally to around 4000 or 5000.
This is similar to decay—the intensity increases as the value decreases. To increase the chances that indirect light will reach a greater distance, decrease the value.
Visible noise can occur with values less than 1. The default (2) simulates natural (quadratic) decay, but violates the conservation-of-energy law (that happens in the natural world), so bright spots from distant light sources could occur in unexpected locations.
The number of photons to be generated by the light source and therefore stored in the photon map. The default, 10000, is suitable for quick, low-quality caustics. To improve the quality of caustic effects, increase this number, incrementally, to 20000 to start (render time will increase as a result). Generally, 100000 produces medium quality and 1000000 produces highly accurate effects.
Select between Regular Shadow Map and Detail Shadow Map. For more information, see mental ray shadow maps.
The Bias attribute applies the specified Bias value on a per-light basis, resulting in a slight offset to the shadow depths, and a slightly shifted shadow. This option is useful in tuning shadows in specific cases, such as when rendering Maya® Fur™.
When the per-light Bias attribute is set to 0, the general Shadow Map Bias setting in the Render Settings (Render Settings window, Options tab, mental ray Overrides section, Shadow Map sub-section) is used. When the per-light Bias is a value greater than 0, the specified per-light Bias value is used.
The bias value should typically be smaller than the smallest distance between a shadow caster and a shadow receiver. However, bias values that are too small may cause self-shadowing artifacts.
Determines the distance required between two depth values in a sample, in order for the values to be considered distinct. Setting a very low accuracy value results in larger memory and resource requirements, but increases quality. Setting a very high accuracy value leads to visible artifacts. If this is set to 0, mental ray for Maya determines a reasonable value based on the scene.
