When several photographers are working in close proximity such as a wedding or photography workshop or an event the last thing that you want is for your master speedlite, controller or transmitter to be firing off everyone else’s speedlites. This doesn’t usually happen when using optical wireless since the master speedlite needs to be pointing directly at the slave speedlites and you always need to maintain a line-of-sight between master and slave. Optical wireless also has a short range of around 10m outside. However when you use radio wireless the radio signal can travel much further. Canon states their radio wireless system has a range of 30m but in practice it’s much further. Yongnuo and Godox both claim a radio range of 100m. This means that photographers in the next room or even the next building could be firing your flash accidentally and vice versa. To prevent this each wireless system can be set to a slightly different frequency or channel. Only transmitters and receivers set to the same channel will work together.
Canon’s optical EX wireless system offers 4 optical channels to choose from. Their radio RT wireless system offers 15 different radio channels.
As default the channel will be set to Channel 1 but if you are planning on shooting near other photographers who could be using the same wireless system then it’s a good idea to select a different channel to avoid any conflict or interference.
Godox uses the same Canon EX optical wireless system with the ability to select from one of 4 optical channels. Their Radio X system allows you to select from one of 32 radio channels.