Decimen Lets You Send Files Through Light, Not a Network

I’m not sure when I’d use this, but its a neat concept

Decimen is an open-source web app that moves files between devices through an animated QR stream, requiring no direct network connection, pairing, account, or native app.

linuxiac.com/decimen-lets-you-send-files-through-light-not-a-network/

A relatively similar tech, though no actual graphics are involved like QR-code images, and hence may be more energy efficient, is of course - Infrared Data Association (IrDA).

Some may still recall the Symbian, music/picture/game files transferred slowly but awesomely between friends/partners watching devices carefully aligned on windowsills, tables…

IrDA is a wireless standard designed for data transmission using infrared (IR). Infrared ports for this purpose have been implemented in portable electronic devices such as mobile telephones, laptops, cameras, printers, and medical devices.

The main characteristics of this kind of wireless optical communication are short-range, physically secure and bidirectional data transfer, at serial cable speeds, with a line-of-sight using point-and-shoot principles. IrDA has been made dormant by newer improved technologies like Bluetooth.

Source: en.wikipedia.org/wiki/IrDA