What are the lights on my laptop? Why are they blinking?

So there are 4 lights on my laptop as seen in the image.
WHEN MY LAPTOP IS OPEN AND THE CHARGER IS PLUGGED IN
The 2nd one is always on, the 1st one is always on, the 3rd one is off, the 4th one blinks really short, but not often
WHEN MY LAPTOP LID IS CLOSED
They are all off except the 1st one which blinks every second.
BTW, this is a Lenovo Y50.
Can someone explain what each light means and why it blinks? Added (1). When my laptop is closed and charger is in, the 2nd light stays on, all others are off except the first one which blinks once a second.