Present participle of diffuse; the action of spreading or scattering something gradually, or (as adjective) that spreads or scatters.
From diffuse + -ing (present participle suffix). The -ing suffix derives from Old English and is one of the most productive verb suffixes, creating nouns and adjectives from verb stems.
Diffusing light is actually a delicate engineering problem—too much diffusion and you lose brightness, too little and you get harsh shadows, which is why lighting designers obsess over diffusing materials.
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