Sekigahara vs Light Red

How close are they?

ΔE 29.8, loose: different enough that you should pick on purpose. Light Red is much more saturated, warmer than Sekigahara.

Can I use Light Red instead of Sekigahara?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Light Red is much more saturated, warmer than Sekigahara.

Can I use Sekigahara instead of Light Red?

The same difference applies the other way round: Sekigahara is 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.