Fluorescent Orange vs Fluorescent Red

How close are they?

ΔE 20.4, loose: different enough that you should pick on purpose. Fluorescent Red is more muted, cooler than Fluorescent Orange.

Can I use Fluorescent Red instead of Fluorescent Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Fluorescent Red is more muted, cooler than Fluorescent Orange.

Can I use Fluorescent Orange instead of Fluorescent Red?

The same difference applies the other way round: Fluorescent Orange is 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.