I wanted to export the lighting component of a mesh as a light map for use in a game, so I've scripted a 3ds Max script to automate the creation of hundreds of lightmaps. However the generated image is as it appears in the render window - it is the complete map, not just the lighting component.
Your max script may look like the following - replace the lm.fileType with the full path instead of just the extension, do not pass in the outputFile to the render call.
local lm = LightingMap()
lm.outputSzX = 100
lm.outputSzY = 100
lm.autoSzOn = off
lm.fileType = ".png"
lm.fileType = "C:\Full\Path\To\Output\Dir\Lightmap1.png"
lm.shadowsOn = on
lm.directOn = on
lm.indirectOn = on
lm.enabled = on
bakeProps = obj.INodeBakeProperties
bakeProps.bakeEnabled = true
bakeProps.flags = 1
bakeProps.bakeChannel = 3
bakeProps.nDilations = 16
bakeProps.addBakeElement lm
local renderedMap = render \
rendertype:#bakeSelected \
outputwidth: lm.outputSzX \
outputheight: lm.outputSzY \
vfb:on \
outputFile: outputPath\
filterMaps:on \
antiAliasFilter:(catmull_rom())