Capo on 4th fret.
Then C/G2 is going to be the same shape, but starting at the 4th fret.
Sounds like the way Lights plays it most when you hammer on with the Em and hammer on 
the D-string when playing the C/G variation chord.
~~~~~~~~~~~~~
C/G, Em, C/G, Em, C/G2    (2x)

C/GWhere (3x555x@1)the fence is low
                 EmAnd (022000@1)the water is rising
C/GAnd (3x555x@1)the fire comes down
                       Em (022000@1)  C/G2
And the dark fills the skies in
C/GOne (3x555x@1)foot on the ledge
                    EmAnd (022000@1)I'm feeling for safety
C/GSomewhere (3x555x@1)between sure
            Em (022000@1)  C/G2
And I don't know, maybe

GI'm (320003@1)off of my rope here
C/GI'm (3x555x@1)off on my own here
GI (320003@1)find my hope here
C/GI (3x555x@1)find my own here
EmI'm (022000@1)off of my rope here
C/GWhere (3x555x@1)the fence is low
G (320003@1)                C/GWhere (3x555x@1)the fence is low
G (320003@1)                C/GWhere (3x555x@1)the fence is low

C/G (3x555x@1)                              EmIn (022000@1)shadow I walk to the ends of the forest
C/GAnd (3x555x@1)the shape of the hands
Em (022000@1)                  C/GThat (3x555x@1)break the ground for us
C/G (3x555x@1)                                  EmThe (022000@1)fear that contains the binds like a blessing
C/GI've (3x555x@1)been here before
            Em (022000@1) C/G2
Then again, I'm guessing

GI'm (320003@1)off of my rope here
C/GI'm (3x555x@1)off on my own here
GI (320003@1)find my hope here
C/GI (3x555x@1)find my own here
EmI'm (022000@1)off of my rope here
C/GWhere (3x555x@1)the fence is low
G (320003@1)               C/GWhere (3x555x@1)the fence is low
G (320003@1)               C/GWhere (3x555x@1)the fence is low

G (320003@1)                C/GLow, (3x555x@1)low, low, low

GI'm (320003@1)off of my rope here
C/GI'm (3x555x@1)off on my own here
GI (320003@1)find my hope here
C/GI (3x555x@1)find my own here
EmI'm (022000@1)off of my rope here
GWhere (320003@1)the fence is low