A reflector for reflecting light from an elongate light source into the input end of a light guide having a diameter "D". The light source is inserted through the narrow end of a collimating reflector which has a wide end with a diameter exceeding "D" through which light is emitted into the guide. The wide end of an output reflector circumferentially surrounds the collimating reflector's wide end. The output reflector's narrow end circumferentially surrounds the light guide's input end. The wide end of an input reflector circumferentially surrounds the collimating reflector's narrow end. The reflectors are cylindrically symmetrical about a common axis. Light passing from the light source to the collimating reflector is reflected, producing an output beam whose width varies as a function of distance along the axis. The light guide's input end is positioned along the axis to minimize the width of the output light beam.