Diagnosis
The BE800 has a customizable LED matrix that's pretty bright by default. It's designed to show status, but you have full control to dim or disable it.
How to Fix It
The easiest way is through the Tether app. Open the app, select your router, and look for a settings icon or 'Tools' menu. There should be an option called 'LED Control' or 'Light Effect'. In there, you can set it to 'Off', 'Dim', or schedule it to turn off during certain hours. You can also change the colors and patterns if you want it subtle.
If That Didn't Work
You can also do it from the web interface. Log in at tplinkwifi.net, go to 'Advanced', then 'System Tools', and look for 'LED Control'. The setting is in there.
Heads Up
If you turn the LEDs completely off, you lose the visual status cues (like an amber boot error light). Consider setting a schedule to turn them off only at night, or just dimming them to 10% so you can still see if there's a problem.