ΔE 17.3, loose: different enough that you should pick on purpose. Light Gray is a little darker, much more saturated than Longbeard Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Light Gray is a little darker, much more saturated than Longbeard Grey.
The same difference applies the other way round: Longbeard Grey is a little lighter, 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 Longbeard Grey on the colour wheel See Light Gray on the colour wheel
All matches: Longbeard Grey equivalents · Light Gray equivalents