Bismuth Yellow vs Light Yellow

How close are they?

ΔE 7.5, close: similar, with a visible difference side by side. Light Yellow is more muted than Bismuth Yellow.

Can I use Light Yellow instead of Bismuth Yellow?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Light Yellow is more muted than Bismuth Yellow.

Can I use Bismuth Yellow instead of Light Yellow?

The same difference applies the other way round: Bismuth Yellow is 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.