What do the LED lights on the AC750 Range Extender mean?

The Power LED shows if the extender is on (solid green) or booting (solid amber). The Router LED indicates the connection between the extender and router—solid green is best, amber is good, red is poor, and off means no connection. The Device LED shows the connection between the extender and your devices with the same color coding. The WPS LED is solid green when WiFi security is enabled, blinks green during WPS connection, and is off when security is disabled.