  We consider the energy and helicity densities of circularly polarised light
within a lossless chiral medium, characterised by the chirality parameter
$\beta$. A form for the helicity density is introduced, valid to first order in
$\beta$, that produces a helicity of $\pm\hbar$ per photon for right and left
circular polarisation, respectively. This is in contrast to the result obtained
if we use the form of the helicity density employed for linear media. We
examine the helicity continuity equation, and show that this modified form of
the helicity density is required for consistency with the dual symmetry
condition of a chiral medium with a constant value of ${\epsilon}/{\mu}$.
Extending the results to arbitrary order in $\beta$ establishes an exact
relationship between the energy and helicity densities in a chiral medium.
