Switch Lights

I was wondering if someone could briefly identify what the LED lights on a switch or on a NIC represent. I always thought they represented packet collisions and corrections or something along those lines. A very brief answer or link to an article would be greatly appreciated.

Thanks!

generally its just activity (like packets going through it)

depends on the model. a lot of times it will also show what speed the connection is at (ie orange denotes 100mbps while green denotes 1000mbps)

again it all depends on the model