little green lights?

[7gmc2]

i have been trying to figure out now for sometime just what the little green lights are that are in the top right corner of a thread besides number of posts. at first i thought it had to do with the actual number of posts that you had made, but i found that not to be the case. then there is the fact that some of the lights are lit and some are not. when you move your mouse pointer on the lights it says different things on the lights for different people. just what does this all mean and what are the lights for anyway?