Diagnosis
The LEDs are indeed quite bright, especially in a dark room. Asus built in a way to turn them off, but it's not a physical switch.
How to Fix It
You control the LEDs through the web interface or app. 1) Log into router.asus.com or open the Asus Router app. 2) Navigate to General -> Network Tools -> LED. 3) You'll see options to turn the LED On, Off, or on a schedule. Select Off and apply. This turns off the light on all nodes.
If That Didn't Work
If the setting doesn't stick after a reboot, it's a known firmware glitch sometimes. Make sure your system is updated to the latest firmware via the Administration -> Firmware Upgrade section, then try the LED setting again.
Heads Up
With the lights off, you lose the visual status indicator. A solid white light means good, red means problems, flashing means booting. You'll have to rely on the app to check node status if the lights are off.