On 5/8/2014 5:18 PM, James wrote:

snip

Oh, you mean a torch. Those things should be banned on road bikes,
unless there is a switch to use them as high beam only with a properly
shaped low beam light for normal urban use. Ultra bright poorly
directed torch lights are a hazard to the user and others around them.

Untrue. All the experts agree that a symmetrical beam is as close to
ideal as you're likely to get for bicycle lights.

While some people may aim their light to high, they can do this with any
light, bicycle-specific or not. And of course many bicycle specific
lights have symmetrical beams anyway.

Old style, low power, bicycle lights often have a beam with a horizontal
cutoff that directs the limited available light onto the road surface
directly in front of the bicycle. These focused beams are a compromise
necessitated by the lack of sufficient power. Unless all of your night
riding takes place on well-lit streets these lights should be avoided
because they do not provide proper illumination for safe riding.

Proper bicycle lights have a beam that's nearly symmetrical. This is for
two reasons. First, because it's critical to cast some light off to the
sides so vehicles approaching from the right or left can see you coming.
Second, because it's vital to have some light shine slightly up in order
to see overhead obstacles such as tree branches, and to read street signs).