ΔE 11.0, fair: the same colour family, but not a straight swap. Chestnut Brown is more muted, cooler than Light Umber.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Chestnut Brown is more muted, cooler than Light Umber.
The same difference applies the other way round: Light Umber is more saturated, 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.
See Light Umber on the colour wheel See Chestnut Brown on the colour wheel
All matches: Light Umber equivalents · Chestnut Brown equivalents