If you could get a circuit to oscillate quickly enough, could visible light be produced using a simple metallic antenna?
The question is, could you get a circuit to oscillate fast enough?
Could we manufacture an antenna and system on scale to resonate at visible light?
Generally the classical electromagnetic theory holds well until around the Terahertz range. From there, it is usually best to use quantum electrodynamics with a mix of classical electromagnetics when appropriate. So if you want to design a device that radiates visible light, classical EM would give you a device that is physically unrealizable. Quantum electrodynamics gives you options like black body radiators or emmission from excited states that can be used to design real devices that will emit visible light. This can vary from heating the tungsten wires in your incadescent lights to flourescent lights or even light emitting diodes or transistors (I am not sure if they have gotten the LET into visible light region yet, my understanding from the talks that I attended a few years ago is that the LET was only recently invented).
I am fairly conviced that ordinary vibratory dynamics or standard electromagnetic theory cannot do this, but is there some QED concept that can be used here, i am sorry i did not follow the post on the QED part can some one make it a little more verbose