The effect of long scale-length irradiation non-uniformities on the implosion of two different directly driven, gas filled shells (representative of large families of laser fusion targets) is studied by means of 2-D numerical fluid simulations. Quantitative results are given for parameters measuring the shell deformation and the azimuthal variation of the (density × radius) product (<ρR) as functions of the wavelength and of the amplitude of the irradiation non-uniformity. The reflection of the imploding shock wave is also qualitatively illustrated.