A beam angle – also referred to as a beam spread – is a measurement of how light is distributed. On any plane vertical to a light’s centerline, beam angle is the angle between two light rays with the light intensity equal to 50% of the maximum light intensity. The larger the beam angle, the smaller the central light intensity, and the larger the light spot. In general, a narrow beam is a beam angle of less than 20°; a medium beam is a beam angle of 20° to 40°, and a wide beam greater than 40° (Figure 1.5.1).
Beam angle lamps of different sizes give off dispersed lighting effects differently. Therefore, what needs to be considered in lighting design is to choose the right beam angle according to specific needs. Lamps with a distinctive beam angle are mostly applied to focused lighting, intended to highlight the focal point, such as decorative paintings, artwork, etc.