Phthalo Turquoise Light vs Light Emerald

How close are they?

ΔE 21.1, loose: different enough that you should pick on purpose. Light Emerald is a little darker, more saturated, warmer than Phthalo Turquoise Light.

Can I use Light Emerald instead of Phthalo Turquoise Light?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Light Emerald is a little darker, more saturated, warmer than Phthalo Turquoise Light.

Can I use Phthalo Turquoise Light instead of Light Emerald?

The same difference applies the other way round: Phthalo Turquoise Light is a little lighter, 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.