Lunar Eclipse vs Crimson Magenta

How close are they?

ΔE 19.3, loose: different enough that you should pick on purpose. Crimson Magenta is noticeably lighter, more saturated, warmer than Lunar Eclipse.

Can I use Crimson Magenta instead of Lunar Eclipse?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Crimson Magenta is noticeably lighter, more saturated, warmer than Lunar Eclipse.

Can I use Lunar Eclipse instead of Crimson Magenta?

The same difference applies the other way round: Lunar Eclipse is noticeably darker, more muted, 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.