  We estimate the amplitude of perturbation in dark energy at different length
scales for a quintessence model with an exponential potential. It is shown that
on length scales much smaller than hubble radius, perturbation in dark energy
is negligible in comparison to that in in dark matter. However, on scales
comparable to the hubble radius ($\lambda_{p}>1000\mathrm{Mpc}$) the
perturbation in dark energy in general cannot be neglected. As compared to the
$\Lambda$CDM model, large scale matter power spectrum is suppressed in a
generic quintessence dark energy model. We show that on scales $\lambda_{p} <
1000\mathrm{Mpc}$, this suppression is primarily due to different background
evolution compared to $\Lambda$CDM model. However, on much larger scales
perturbation in dark energy can effect matter power spectrum significantly.
Hence this analysis can act as a discriminator between $\Lambda$CDM model and
other generic dark energy models with $w_{de} \neq -1$.
