Radiation Glow vs Naples Yellow

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Naples Yellow is a little lighter, more saturated, cooler than Radiation Glow.

Can I use Naples Yellow instead of Radiation Glow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Naples Yellow is a little lighter, more saturated, cooler than Radiation Glow.

Can I use Radiation Glow instead of Naples Yellow?

The same difference applies the other way round: Radiation Glow is a little darker, more muted, warmer.

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.