The beam angle of a lighting source is the angle between the two opposing points at which the light output from the light source drops to below 50% intensity. A simplified way of thinking about the beam angle of a light source is that it is the angle at which light will be emitted from a lighting source.
As a general guide for household lighting applications Light Bulbs within the range of 20 to 45 degrees are suitable. A lower beam angle will provide you with a more focused light output, whilst a higher beam angle will flood a larger area with light than smaller angles can.
Considering the beam angle is an important part of the process of buying lighting products, as the right beam angle will provide you with the optimum amount of light, and may even provide you with some vital energy savings.