Thanks for the reply. Sorry for taking so long to get back. My Luxeon III MR16 is from http://autolumination.com/mr16.htm. At the time they only offered it in one color, which is fairly bluish so I presume it's the "cool white". It was advertised as having a 100 degree beam, though in practice the majority of light is concentrated into a 15 degree beam where you want it. There's significant overspill beyond 15 degrees, which is actually very nice and provides decent peripheral vision on dark pathways, with a very sharp edge to the beam at about 100 degrees.

Overall light output seems equivalent to a 5-6W halogen, though still less than a 10W. It puts out noticeably a bit less light than my Priceton Tec Apex headlamp, also a Luxeon III but a particularly well designed one. Still noticeably more light than the 1W Luxeon Princeton Tec Eos I use on my helmet. It's enough to light up your path in low light situations at moderate speeds, and still enough to be visible on the pavement in most lighted streets.

I measured the effective current draw at about 4 watts, so it's clearly not the most efficient LED assembly out there. But it's still more efficient than a low-wattage halogen, it's just the right amount of light for my low beam needs, and the beam shape is absolutely perfect, so I'm very happy with it.