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.

The angle between the two directions in the plane in which the intensity is equal to a given percentage (usually 10 percent) of the maximum beam intensity.

The divergence of the sound beam as it travels through a medium. Specifically, the solid angle that contains the main lobe of the beam in the far field.

A measure of the spread of light from a reflectorized light source. The beam spread may be narrow (narrow spot), wide (wide flood), or something in-between (narrow flood).

The total angle of the directed beam to where the intensity of the beam falls to 50% or 10% of the maximum candlepower value as indicated.

Microscale eddies, smaller than or about the same size as the beam width, which increase the cross-sectional area of the beam and decrease the intensity of its energy.

The diameter of the pattern of light produced by a lamp or lamp and luminaire together.

Lighting term: the area that a given lantern covers. It is usually expressed as the angle that the beam subtends at the focal plane: the smaller the angle, the narrower the beam.

The width of a light beam, expressed in degrees. The beam of light from a reflector-type lamp (PAR, R, ER, or MR) can be thought of as a cone. The beam spread is the angular width of the cone. Common beam spreads are known as spot, narrow, narrow flood, and flood.

The width of the light aiming out of a bulb.

In any plane, the angle between the two directions in the plane in which the candlepower is equal to a stated percent of the maximum candlepower in the beam.

A measure of the angle of the light beam from a lamp with a reflector. This might be narrow spot, narrow flood, or wide flood.

The angle enclosed by two lines which intersect the candlepower distribution curve at the points where the candlepower is equal to ten percent of its maximum.