Radiation angle

Radiation angle: In fiber optics, half the vertex angle of the cone of light emitted at the exit face of an optical fiber.

Note: The cone boundary is usually defined (a) by the angle at which the far-field irradiance has decreased to a specified fraction of its maximum value or (b) as the cone within which there is a specified fraction of the total radiated power at any point in the far field.

Synonym output angle.

Source: from Federal Standard 1037C and from MIL-STD-188