ΔE 26.5, loose: different enough that you should pick on purpose. Light Yellow is noticeably darker, much more saturated, warmer than Lemon Yellow.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Light Yellow is noticeably darker, much more saturated, warmer than Lemon Yellow.
The same difference applies the other way round: Lemon Yellow is noticeably lighter, much more muted, cooler.
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 Lemon Yellow on the colour wheel See Light Yellow on the colour wheel
All matches: Lemon Yellow equivalents · Light Yellow equivalents