ΔE 18.3, loose: different enough that you should pick on purpose. Iridescent Copper Light (Fine) is a little lighter, much more saturated than Emperor Gold. They are different kinds of paint: Army Painter Emperor Gold is a metallic and Golden Iridescent Copper Light (Fine) is a pearl 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 18). Iridescent Copper Light (Fine) is a little lighter, much more saturated than Emperor Gold. They are different kinds of paint.
The same difference applies the other way round: Emperor Gold is a little darker, much more muted.
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 Emperor Gold on the colour wheel See Iridescent Copper Light (Fine) on the colour wheel
All matches: Emperor Gold equivalents · Iridescent Copper Light (Fine) equivalents