Naphthol Red Light vs Ink Red

How close are they?

ΔE 15.4, loose: different enough that you should pick on purpose. Ink Red is noticeably darker, more saturated than Naphthol Red Light.

Can I use Ink Red instead of Naphthol Red Light?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Ink Red is noticeably darker, more saturated than Naphthol Red Light.

Can I use Naphthol Red Light instead of Ink Red?

The same difference applies the other way round: Naphthol Red Light is noticeably lighter, 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.