How do I turn off backlight of keyboard?

I've tried xset led 3, xset led off, xbacklight -set 00,

sudo find /sys/devices/platform/ -name leds returns nothing, so I couldn't try that.

sudo find /sys/devices -name leds returns /sys/devices/pci0000\:00/0000\:00\:1c.5/0000\:3f\:00.0/leds, but sudo echo '0' > /sys/devices/pci0000\:00/0000\:00\:1c.5/0000\:3f\:00.0/leds/phy0-led/brightness returns permission denied (yes, even with sudo).

sudo xmodmap -e 'add mod3 = Caps_Lock' returns error

X Error of failed request: BadValue (integer parameter out of range for operation) Major opcode of failed request: 118 (X_SetModifierMapping) Value in failed request: 0x17 Serial number of failed request: 11 Current serial number in output stream: 11

So, I pretty much just copied and pasted a bunch of solutions from stack overflow, and so far nothing has worked, although, this, I believe should be a very simple thing to do.

I'm on a Lenovo Yoga 720, running ubuntu 18.10.