Bright Green vs Goblin Green

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Goblin Green is a little lighter, more saturated, warmer than Bright Green.

Can I use Goblin Green instead of Bright Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Goblin Green is a little lighter, more saturated, warmer than Bright Green.

Can I use Bright Green instead of Goblin Green?

The same difference applies the other way round: Bright Green is a little 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.