Contrary to this nodeshell's title, if you play a note high enough, it will not become a beam of light.

Let's look at a modern piano, for example. Its eighty-eight keys can play every note between an A0 and a C8. This means it can vibrate strings, and therefore air, at between 27.5Hz and 4186.01Hz. Simply put, it can move air back and forth between 27.5 and 4186.01 times every second. We can hear air vibrating between 20Hz and 20,000Hz, so we can hear every note of a piano.

Now let's look at light. We can see electromagnetic radiation with a frequency of between 405,000,000,000,000Hz (red) and 790,000,000,000,000Hz (violet). That's much faster than the strings of a piano, but if it were possible to vibrate strings that quickly, you might think you would be able to see them shining a vibrant colour.

Sadly, this isn't the case. The difference isn't just the frequency, it's the thing that's vibrating. Moving air back and forth is very different from giving off electromagnetic energy. Regardless of the speed you do it at, our ears can only hear air moving back and forth, and our eyes can only see electromagnetic radiation. This means you will never see a note, regardless of how high it is.

References: I shamelessly looked the frequencies up in Wikipedia, namely the pages and