  We investigate the signature of the photospheric albedo contribution in solar
flare hard X-ray spectra, the effect of low energy cutoffs in electron spectra,
and the directivity of hard X-ray emission. Using Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) flare data we perform a statistical analysis of
spatially integrated spectra and positions of solar flares. We demonstrate
clear centre-to-limb variation of photon spectral indices in the 15-20 keV
energy range and a weaker dependency in the 20-50 keV range which is consistent
with photospheric albedo as the cause. The results also suggest that low-energy
cutoffs sometimes inferred in mean electron spectra are an artefact of albedo.
We also derive the anisotropy (ratio of downward/observer directed photons) of
hard X-ray emission in the 15-20 keV range for various heliocentric angles.
