  While solar flares are predominantly characterised by an intense broadband
enhancement to the solar radiative output, certain spectral lines and continua
will, in theory, exhibit flare-induced dimmings. Observations of transitions of
orthohelium He I $\lambda\lambda 10830${\AA} and the He I D3 lines have shown
evidence of such dimming, usually followed by enhanced emission. It has been
suggested that non-thermal collisional ionisation of helium by an electron
beam, followed by recombinations to orthohelium, is responsible for
overpopulating the those levels, leading to stronger absorption. However it has
not been possible observationally to preclude the possibility of overpopulating
orthohelium via enhanced photoionisation of He I by EUV irradiance from the
flaring corona followed by recombinations. Here we present radiation
hydrodynamics simulations of non-thermal electron beam-driven flares where (1)
both non-thermal collisional ionisation of Helium and coronal irradiance are
included, and (2) only coronal irradiance is included. A grid of simulations
covering a range of total energies deposited by the electron beam, and a range
of non-thermal electron beam low-energy cutoff values, were simulated. In order
to obtain flare-induced dimming of the He I 10830{\AA} line it was necessary
for non-thermal collisional ionisations to be present. The effect was more
prominent in flares with larger low-energy cutoff values and longer lived in
weaker flares and flares with a more gradual energy deposition timescale. These
results demonstrate the usefulness of orthohelium line emission as a diagnostic
of flare energy transport.
