Purple Rain vs Orchid Light

How close are they?

ΔE 21.3, loose: different enough that you should pick on purpose. Orchid Light is noticeably lighter, more muted than Purple Rain.

Can I use Orchid Light instead of Purple Rain?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Orchid Light is noticeably lighter, more muted than Purple Rain.

Can I use Purple Rain instead of Orchid Light?

The same difference applies the other way round: Purple Rain is noticeably darker, more saturated.

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.