Change the brightness of a light.
Available lights will vary per-device but typically include things like keyboard backlights, LEDs, camera flashlights, display and button backlights.
Despite the maximum being given as 255, many lights will only be on or off, in which case 0 specifies off and any other number specifies on.
Note that turning a light off is not permanent, Android may turn it on at a later time in response to various events on the device.
If you accidentally reduce the display backlight to 0, a reboot should solve the problem.