the bottom one is on at a lower watt for daylight running light, it's dimmer than see in night..it is also the high beam
at night, with the headlight on, the top one is on..(the circular one, projector light)and that is the low-beam..
when high beam is on, both the top and bottom will be on, the bottom one is angled higher, there for it's high beam.
p.s: when high beam is on, fogs are automatically shut off (for GTS standard factory fogs)
hope this helps...