Also, why you can produce radio waves with a simple amplifier circuit and a piece of wire, but need special devices like an LED or a discharge tube to produce light?
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I see good info in here but they don’t really seem to answer the questions properly.
>but you can produce one with a simple metal rod
As others have mentioned an antenna needs to be about the same length as the wavelength you’re trying to transmit. But any AC circuit will generate an electromagnetic field, you can usually detect some at 50 or 60 Hz from the power grid without having a proper antenna.
The reason we cant (read don’t) Is because its really hard and not very effective. Its not easy to get a an electrical circuit to run at the frequencies required to generate light.
>And the other can be focused with a glass lens
Radio frequencies can also be focused by a lens but not a glass one. But anything of a reasonable size will only be able to be used on very high frequencies in the microwave category due to the wavelength of the frequency. Lower frequencies will need a larger lens to actually bend the radio waves. [stack exchange post](https://electronics.stackexchange.com/questions/507895/why-dont-we-use-lenses-for-rf).
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