Wireless internet connections use light in the radio frequency ranges.

If you want to send someone a signal with visible light, you can turn the light on and off to communicate in Morse code. This isn't as time-efficient as using a whole display, but it allows you a lot of flexibility - the receiver can stand anywhere, and the sender can turn the light on and off without worrying whether it is oriented correctly. Computers do something similar. The encoding system is much more complicated than Morse code, but the basic idea of changing how the light is emitted over time to transmit data is the same.

These radio frequency ranges have wavelengths between millimeters and meters (they go longer, but the longer wavelengths usually aren't' used for data channels). For these long wavelengths, many physical barriers are translucent, the way cloudy glass is for visible light. The transition isn't perfect, but we intentionally use an encoding that can handle a little bit of noise so you can still receive those signals.