Deep Violet vs Orchid Light

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Orchid Light is a little darker, more muted, cooler than Deep Violet.

Can I use Orchid Light instead of Deep Violet?

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

Can I use Deep Violet instead of Orchid Light?

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