Hidden LED notification light on Nexus 6 

Nexus 6 has an ambient screen mode but it fails to provide a tap to wake functionality.The way people get to know the notifications is by the presence of the LED.It seems that this facility is absent in Nexus 6.
Hang on!!!!!!!!its not.There is a physical LED that is present behind the speakers/ear piece.It is capable of producing red,blue and green light.However this feature is not enabled by default.You will have to root the phone.

Source:Android Police