Fulgurite Copper vs Light Bronze

How close are they?

ΔE 30.3, loose: different enough that you should pick on purpose. Light Bronze is noticeably lighter, much more muted, cooler than Fulgurite Copper.

Can I use Light Bronze instead of Fulgurite Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Light Bronze is noticeably lighter, much more muted, cooler than Fulgurite Copper.

Can I use Fulgurite Copper instead of Light Bronze?

The same difference applies the other way round: Fulgurite Copper is noticeably darker, much 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.