Luminous Green vs Lemon Yellow

How close are they?

ΔE 20.7, loose: different enough that you should pick on purpose. Lemon Yellow is much more saturated, warmer than Luminous Green.

Can I use Lemon Yellow instead of Luminous Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Lemon Yellow is much more saturated, warmer than Luminous Green.

Can I use Luminous Green instead of Lemon Yellow?

The same difference applies the other way round: Luminous Green is much 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.