Okay...
Just make a coil/capacitor combo set for the frequency of visible light.
(Frequencies: 4 - 7.5 x 10^14 Hz)
http://hyperphysics.phy-astr.gsu.edu/hbase/ems3.html

How to Build:

https://www.youtube.com/watch?v=VqdcU9ULAlA

https://www.youtube.com/watch?v=9VqVaFMQd2o

How it Works:

https://www.youtube.com/watch?v=0-PParSmwtE

Misc:

https://www.youtube.com/watch?v=gcui0K7JZXA

Interesting.  That coil looks a lot like my Slayer Exciter coil which resonates at about 586kHz.
http://open-source-energy.org/?tid=1243