LDM is a precalculated map with small scale indirect illumination effects, it can be combined with realtime GI solvers and with constant ambient mode.
LDM defines the geometry with a low level Ambient Occlusion pre-calculated map. Unwrapping and LDM baking is needed in order to activate this feature.
LDMs.. are fully interactive with radiosity and direct illumination, while baking RENDERLights will create a separate folder for all of the
LDMs maps that have been created during the baking process.
Explorer tree / Static Objects / Build LDMs...
An example of LDM can be appreciated on this Toy Train, the first image is only using Constant ambient Illumination, while the second image has
been baked to display a LDM map, as mentioned before LDM can be blend with Precalculated and Realtime radiosity modes.