DIAGNOSIS: Yeah, this one's common and annoying. The white LED indicates the monitor is in standby mode (receiving power but no signal). There's no physical way to turn it off, but you can dim it or change its behavior.
FIX: Use the joystick button to enter the OSD menu. Navigate to Others > Power LED. Here, you can set it to Dimmed, which will make it much less bright when the screen is off. That's the best you can do for a softer glow.
IF THAT DIDN'T WORK: If the dimmed setting is still too bright for a dark room, your only option is to physically cut power to the monitor by using a smart plug or switching off the power strip it's plugged into. This is less than ideal, as it prevents the monitor from receiving firmware updates or remote wake-up signals.
HEADS UP: A solid white light is normal. If the LED is blinking white, that usually indicates the monitor is in self-test mode or trying to detect a signal. A blinking amber light typically means it's receiving a signal but is in power-saving mode.