Visible light cannot be generated using switched or oscillating currents with today's technology.
I believe that THz radiation, with wavelengths on the order of 0.1 to 1 mm, is the closest that has been generated using high frequency currents. This band is also called submillimeter radiation, and barely reaches the far infrared range. Various high frequency RF, microwave and millimeter wave techniques have been used to generate THz radiation, including backward wave oscillators (BWO), gyratrons, and frequency multipliers using diodes or varactors.
In addition, laser based techniques such as photomixing and photconductive switching have been used. Photomixing uses two IR lasers with separate frequencies illuminating a semicondutor that produces a difference frequency in the THz range by conductivity modulation.
Photoconductive switching uses a laser generated, compressed, short optical pulse on the order of a femtosecond, applied across a small gap between conductors bridged by a semicondutor to produce a current pulse. The resulting current either exites an antenna directly, or is applied to a device to be tested. Another photoconductive device can be used as a detector. This technique is used in time-domain spectroscopy for study of material properties in the terahertz range.
The power level generated by these techniques is generally quite small ($\mu$W, or lower), so their practical use is limited.