How can I turn off the lights on my Logitech G413 SE keyboard?

I got a Logitech G413 SE keyboard. Its keys are lit when I plug it in; I want to turn that light off; but - there is no "lights off" switch on it! Damn them. Logitech has all sorts of software to do this on Windows. But - how can I turn off the lights on a Linux system? I'd prefer something that can work even from the command-line, but even a closed-source GUI utility is better than nothing... My distribution: Devuan GNU/Linux Daedalus.