Open "Displacement Comparison" iClone 6 demo project (you may open any other project with props featuring fairly complex displacement maps)
Do the Iray render preview (note Light hierarchy initialization is at 0.00 seconds)
Add any Glow map to both planes at the scene (glow strengthen does not matter)
Do the Iray render preview again (note Light hierarchy initialization went to 82 seconds)
Such delay at "Lights Hierarchy Initialization" is only justified if the scene has 1000s of light sources.
It looks like Displacement map splits a Glow map light into multiple sources (at least it seems)...
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