Deep Violet vs Light Violet

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Light Violet is a little darker, much more muted, cooler than Deep Violet.

Can I use Light Violet instead of Deep Violet?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Light Violet is a little darker, much more muted, cooler than Deep Violet.

Can I use Deep Violet instead of Light Violet?

The same difference applies the other way round: Deep Violet is a little 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.