Arcane Blue vs Light Blue Green

How close are they?

ΔE 21.1, loose: different enough that you should pick on purpose. Light Blue Green is noticeably darker, cooler than Arcane Blue.

Can I use Light Blue Green instead of Arcane Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Light Blue Green is noticeably darker, cooler than Arcane Blue.

Can I use Arcane Blue instead of Light Blue Green?

The same difference applies the other way round: Arcane Blue is noticeably lighter, warmer.

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.