  Recent cosmological observations indicate that the present universe is flat
and dark energy dominated. In such a universe, the calculation of the
luminosity distance, d_L, involve repeated numerical calculations. In this
paper, it is shown that a quite efficient approximate analytical expression,
having very small uncertainties, can be obtained for d_L. The analytical
calculation is shown to be exceedingly efficient, as compared to the
traditional numerical methods and is potentially useful for Monte-Carlo
simulations involving luminosity distances.
