  Synthetic chiral light fields were recently introduced as a novel source of
chirality [Ayuso et al. Nat. Phot. 13, 866 (2019)]. This locally-chiral light
spans a three-dimensional polarization that plots a chiral trajectory in
space-time, leading to huge nonlinear chiral signals upon interactions with
chiral media. The degree of chirality of this new form of light was defined,
characterized, and shown to be proportional to the chiral signal conversion
efficiency. However, the sign of the light's chirality - its 'handedness' - has
not yet been defined. Standard definitions of helicity are inapplicable for
locally-chiral light due to its complex three-dimensional structure. Here, we
define an unambiguous handedness for locally-chiral fields and employ it in
practical calculations.
