Light Red vs Magenta Blood

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Magenta Blood is a little darker, more saturated than Light Red.

Can I use Magenta Blood instead of Light Red?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Magenta Blood is a little darker, more saturated than Light Red.

Can I use Light Red instead of Magenta Blood?

The same difference applies the other way round: Light Red is a little lighter, 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.