Cobalt Green vs Light Emerald

How close are they?

ΔE 20.1, loose: different enough that you should pick on purpose. Light Emerald is noticeably lighter, more saturated, cooler than Cobalt Green.

Can I use Light Emerald instead of Cobalt Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Light Emerald is noticeably lighter, more saturated, cooler than Cobalt Green.

Can I use Cobalt Green instead of Light Emerald?

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