The three lights on the left hand side tell what shape the battery is in, and the three on the right are for the alternator function...on that side, only the yellow and green are supposed to light up or else the Alt. would be "overcharging" the battery....
On my bike, the alternator starts charging fully at around 800-1000 RPM...so, if you have a lot of electrical draw on your bike and just sit at a redlight, it'll be draining the battery until you give it a little throttle, thus the headlights dim at idle and brighten back up as the Alt. kicks back in....
