Radiant Yellow vs Light Yellow

How close are they?

ΔE 8.4, close: similar, with a visible difference side by side. Light Yellow is a little darker than Radiant Yellow.

Can I use Light Yellow instead of Radiant Yellow?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Light Yellow is a little darker than Radiant Yellow.

Can I use Radiant Yellow instead of Light Yellow?

The same difference applies the other way round: Radiant Yellow is a little lighter.

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.