Definitions for "Beam Spread"
The width of the light beam from a reflector, the edge defined by the point at which light intensity is 50% of the maximum
The angle of a beam from a light source to the main area lighted; more specifically, the angle between the two vectors in which the light output is equal to a stated percent (usually 10%) of the maximum candlepower of the source.
The angle (in the plane through the beam axis) over which the luminous intensity drops to a stated percentage of its peak intensity.