Fire Red vs Light Red

How close are they?

ΔE 32.3, loose: different enough that you should pick on purpose. Light Red is noticeably lighter, much more saturated, warmer than Fire Red.

Can I use Light Red instead of Fire Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Light Red is noticeably lighter, much more saturated, warmer than Fire Red.

Can I use Fire Red instead of Light Red?

The same difference applies the other way round: Fire Red is noticeably darker, much more muted, cooler.

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.