Gladeshard vs Bright Green

How close are they?

ΔE 34.4, loose: different enough that you should pick on purpose. Bright Green is noticeably darker, much more muted, cooler than Gladeshard.

Can I use Bright Green instead of Gladeshard?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 34). Bright Green is noticeably darker, much more muted, cooler than Gladeshard.

Can I use Gladeshard instead of Bright Green?

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