system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If radio waves and visible light exist on the same spectrum, why can't you tune a transmitter to get it to shine?
gpt
Your antenna isn't efficient at generating waves that small.

Antennas are optimized for a certain size range.  AM antennas are big and transmit around 1 MHz which is waves around 300 meters.  FM antennas can be much smaller and work around 100 MHz / 3 meters.  If you tried to get an antenna that's good at broadcasting FM to instead broadcast 2.4 GHz for WiFi it would do terribly and you'd barely get any signal out no matter how much energy you pumped in.

Similarly a microwave antenna is meant for 300 MHz-300 GHz, trying to get it to blast out Near IR at 400 THz is going to be terribly inefficient, and trying to get it to generate blue light at 770 THz is going to be even worse

You instead need to use transmitters and antennas optimized for the frequency you want to work with, its incredibly hard to build anything that can work effectively across an order of magnitude, let alone 6 (300 MHz to 400 THz)