To answer your question in regards to what is the difference between a D2S and a D2R is that the D2R HID bulb has a metallic strip along one edge to combat unwanted glare in a reflector headlamp housing. The D2S is a clear and naked bulb used in projector-type housing. The LS has a reflector type housing so it comes with a D2R. BMW, Audi who use a projector type assembly use the D2S. They both use the same base and bulb but the D2S does emit slightly more light than the D2R. Lincoln uses the 4100 kelvin rated Philips bulb. Philips and Osram-Sylvania are the most dependable HID bulb manufacturers in the marker. 4100K is daylight white and 6000K is slightly bluish white. Anything higher has more blueness and less brightness. SInce the 4100k is daylight white in color it is least fatiguing on the eyes and produces the most comfortable contrast on the road.