WordReference Random House Unabridged Dictionary of American English © 2025
light•fast 
(līt′fast′, -fäst′),USA pronunciation adj. 
 light′fast′ness, n. 
            - not affected or faded by light, esp. sunlight;
 colorfast when exposed to light.
- light1 + fast1 1955–60
'lightfast' also found in these entries (note: many are not synonyms or translations):