ΔE 29.0, loose: different enough that you should pick on purpose. Light Magenta is noticeably lighter, much more muted, warmer than Impish Rouge.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Light Magenta is noticeably lighter, much more muted, warmer than Impish Rouge.
The same difference applies the other way round: Impish Rouge is noticeably darker, much more saturated, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Impish Rouge on the colour wheel See Light Magenta on the colour wheel
All matches: Impish Rouge equivalents · Light Magenta equivalents