RONJA

thumb|right|Single high-brightness Light-emitting diode|LED with a cheap [[loupe lens creates a bright narrow beam that can stream DVD-quality video over neighbourhoods. The red beam is invisible when observed outside of its unobstructed path.]] thumb|Twibright Ronja with diameter lenses, operating on a link using visible red light, max. range , with HPWT-BD00-E4000 transmitter LED. Installed on a rooftop, with its user posing to the right, in Czech Republic. thumb|right|Three bolts preloaded with pink rubber blocks facilitate fine adjustment of the optical head direction with a gear ratio 1:300. The bolt on the right side is a part of a rough adjustment mechanism which allows pointing the optical head in needed direction. thumb|right|Artificially enhanced picture of fog interfering with a RONJA beam, compromising the connection by introducing interference (communication)|interference

RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system developed in the Czech Republic by Karel Kulhavý of Twibright Labs. Released in 2001. It transmits data wirelessly using beams of light. Ronja can be used to create a 10 Mbit/s full duplex Ethernet point-to-point link. It has been estimated that 1,000 to 2,000 links have been built worldwide.