SAE requires the brightness of Yellow turn signals to be much brighter than the brake lights when measured at different and all locations (Does not make real sense to me, but its true.) I do not think LED's can meet these requirments. Red turn signals are the same brightness as the stop lights since they are physically the same light/bulbs. You will notice that all vehicles (BMW, Mercedes, Acura, Cadillac, etc.) with rear LED turn signals, have red ones that are also the brake lights. I tried to insert an image from the SAE spec, but do not think it worked.