I have been wondering 1. We know that light has a wave-particle duality. Does the "light" here mean electromagnetic radiation, or just visible lights? 2. If it EMR exhibits wave-particle duality, does that mean radio waves are transmitted in form of photons? 3. and finally, I was reading through one of the posts and quoted: Isn't the brightness in visible light dependent on the number of photons the stream of light has? (not the amplitude) Thank you very much!