ΔE 35.3, loose: different enough that you should pick on purpose. Lemon Yellow is a little lighter, much more muted than Neon Yellow. They are different kinds of paint: Army Painter Neon Yellow is a fluorescent or effect paint and Reaper Lemon Yellow is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 35). Lemon Yellow is a little lighter, much more muted than Neon Yellow. They are different kinds of paint.
The same difference applies the other way round: Neon Yellow is a little darker, much 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.
See Neon Yellow on the colour wheel See Lemon Yellow on the colour wheel
All matches: Neon Yellow equivalents · Lemon Yellow equivalents