Dark Emerald vs Light Green RLM25

How close are they?

ΔE 19.4, loose: different enough that you should pick on purpose. Light Green RLM25 is noticeably lighter, more saturated, warmer than Dark Emerald.

Can I use Light Green RLM25 instead of Dark Emerald?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Light Green RLM25 is noticeably lighter, more saturated, warmer than Dark Emerald.

Can I use Dark Emerald instead of Light Green RLM25?

The same difference applies the other way round: Dark Emerald 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.