What diameter beam will a light guide output?

Fiber optic light guides, like optical fibers themselves, do not produce beam-like outputs. They are very good for transmitting light and produce rather quickly diverging cones of light. Due to symmetry principles in fiber optics, the output angle of a fiber is approximately the same as the input angle.

The full acceptance angle is defined as the maximum allowable input/output angle for each light guide and is directly related to the numerical aperture specification (NA). For instance, our typical glass fiber light guides will accept a cone of light approximately 68°, which corresponds to 0.55. Quartz UV light guides have an acceptance angle that is dependant on wavelength and fiber bundle length; for our 36"" length UV guides, the angles are 42° at 254nm and 35° at 546nm for bundles fully illuminated by a source at half intensity. If the input angle, say 30°, is smaller than the acceptance angle, say 68°, then the output angle will still be 30°, not the 68° that one might think. If a fiber is overfilled, the output angle will be slightly less than the acceptance angle due to losses. Using light guides in conjunction with our Fiber-Lite Focusing Lenses will allow the output beam to be focused or collimated.