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Measurements of the HI 21-cm power spectra from the reionization epoch willbe influenced by the evolution of the signal along the line-of-sight directionof any observed volume. We use numerical as well as semi-numerical simulationsof reionization in a cubic volume of 607 Mpc across to study this so-calledlight cone effect on the HI 21-cm power spectrum. We find that the light coneeffect has the largest impact at two different stages of reionization: one whenreionization is $\sim 20\%$ and other when it is $\sim 80\%$ completed. We finda factor of $\sim 4$ amplification of the power spectrum at the largest scaleavailable in our simulations. We do not find any significant anisotropy in the21-cm power spectrum due to the light cone effect. We argue that for the powerspectrum to become anisotropic, the light cone effect would have to make theionized bubbles significantly elongated or compressed along the line-of-sight,which would require extreme reionization scenarios. We also calculate thetwo-point correlation functions parallel and perpendicular to the line-of-sightand find them to differ. Finally, we calculate an optimum frequency bandwidthbelow which the light cone effect can be neglected when extracting powerspectra from observations. We find that if one is willing to accept a $10 \%$error due to the light cone effect, the optimum frequency bandwidth for $k=0.056 \, \rm{Mpc}^{-1}$ is $\sim 7.5$ MHz. For $k = 0.15$ and $0.41 \,\rm{Mpc}^{-1}$ the optimum bandwidth is $\sim 11$ and $\sim 16$ MHzrespectively.

Light cone effect on the reionization 21-cm signal II: Evolution, anisotropies and observational implications