ΔE 24.2, loose: different enough that you should pick on purpose. Light Phthalo Green is much more saturated than White Scar.
Can I use Light Phthalo Green instead of White Scar?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Light Phthalo Green is much more saturated than White Scar.
Can I use White Scar instead of Light Phthalo Green?
The same difference applies the other way round: White Scar is much more muted.
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.