Supercontinuum generation in photonics crystal fibers (PCFs) pumped by CW lasers yields high spectral power density and average power. However, such systems require very high pump power and long nonlinear fibers. By on/off modulating the pump diodes of the fiber laser, the relaxation oscillations of the laser can be exploited to enhance the broadening process. The physics behind the supercontinuum generation is investigated by sweeping the fiber length, the zero dispersion wavelength, and the fiber nonlinearity. We show that by applying gain-switching a high average output power of up to 30 W can be maintained and the spectral width can be improved by 90%. The zero dispersion wavelength should be close to but below the pump wavelength to achieve the most visible light. By increasing the nonlinearity the fiber length can be reduced from 100 m to 25 m and the efficiency of visible light generation is improved by more than 200%.