Electric Blue vs Fluorescent Blue

How close are they?

ΔE 44.7, loose: different enough that you should pick on purpose. Fluorescent Blue is noticeably lighter, more muted, cooler than Electric Blue.

Can I use Fluorescent Blue instead of Electric Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 45). Fluorescent Blue is noticeably lighter, more muted, cooler than Electric Blue.

Can I use Electric Blue instead of Fluorescent Blue?

The same difference applies the other way round: Electric Blue is noticeably darker, 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.