If you've ever wondered why one of the ports on the back of your TV appears to glow, that's the optical digital audio output via a TOSLINK port. It uses light to transmit data through a fiber-optic cable, which is why the port can appear to glow. While HDMI ARC and eARC have become the standard way to connect a TV to speakers, there are still a surprising number of things you can use your optical audio port for.