Pyrrole Red vs Light Red

How close are they?

ΔE 8.6, close: similar, with a visible difference side by side. Light Red is a little lighter, more muted than Pyrrole Red.

Can I use Light Red instead of Pyrrole Red?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Light Red is a little lighter, more muted than Pyrrole Red.

Can I use Pyrrole Red instead of Light Red?

The same difference applies the other way round: Pyrrole Red is a little darker, more saturated.

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.