On 3/24/2017 2:22 AM, Jeff Liebermann wrote:
A properly designed bicycle light or flashlight
should have an even and equal brightness distribution across the spot
on the wall, but this is rarely the case.

A properly designed bicycle light should not have a round spot at all.
See http://peterwhitecycles.com/plight.php for some information on
headlight optics.

Alternately, face your favorite motor vehicle toward a wall, turn on the
lights (low beam) and observe the beam pattern.


--
- Frank Krygowski