Magenta vs Light Pink

How close are they?

ΔE 15.8, loose: different enough that you should pick on purpose. Light Pink is noticeably lighter, much more muted than Magenta.

Can I use Light Pink instead of Magenta?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Light Pink is noticeably lighter, much more muted than Magenta.

Can I use Magenta instead of Light Pink?

The same difference applies the other way round: Magenta is noticeably darker, much more saturated.

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.