Not a duplicate of [this rPi.SE question](http://raspberrypi.stackexchange.com/questions/871/what-do-system-leds-signify), as I'll explain in a moment.

As far as I can tell, looking at my B+, there are no LEDs labeled: `OK`, `FDX`, `LNK` or `10M`. There are two embedded in the Ethernet port, and two on the opposite side of the board. The ones on the Ethernet are unlabeled, but I can guess what they mean. The other two are labeled `ACT` and `PWR`. 

`PWR` only turns on once in a great while. My rPi is running just fine, and the `PWR`  diode is unlit (which others say should never happen). This is the one that confises me the most.

`AMP` seems to turn on under I/O heavy load. (Seems to be the equivalent of the old `OK` LED).

What do these lights signify?