Fluor Violet vs Fluorescent Violet

How close are they?

ΔE 31.6, loose: different enough that you should pick on purpose. Fluorescent Violet is noticeably darker, much more saturated than Fluor Violet.

Can I use Fluorescent Violet instead of Fluor Violet?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Fluorescent Violet is noticeably darker, much more saturated than Fluor Violet.

Can I use Fluor Violet instead of Fluorescent Violet?

The same difference applies the other way round: Fluor Violet is noticeably lighter, much 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.