An easily overlooked concept - Lighting Beam Angle

2023-09-12

The beam angle for one lamp is an important parameter indicator and a manifestation of the lamp's light distribution.

1. Definition of beam angle

According to the "Terminology Standard for Building Lighting" JGJ/T 119-2008, the beam angle is the angle between the two vectors of the luminous intensity curve expressed in polar coordinates on a given plane. The luminous intensity value of this vector is usually equal to the maximum luminous intensity value of 10% or 50%.

From the definition, it can be seen that there is a significant difference between the angle between the 10% maximum light intensity and the 50% maximum light intensity. As shown in Figure 1, the descriptions of different beam angles for the same lamp have multiple differences in numerical values. Therefore, when giving the beam angle value, it should be indicated whether it is the angle between the maximum light intensity of 10% or the maximum light intensity of 50%.

Figure 1 Different descriptions of beam angles

(The angle between the red line is 50% of the maximum light intensity, and the angle between the black line is 10% of the maximum light intensity)

2. Classification of Luminaires by Beam Angle

According to the classification of beam angle, lamps can be divided into narrow distribution, medium distribution, and wide distribution, as shown in Table 1.

Table 1 Classification of Luminaires:

Beam classcification	Beam angle α(°)	Project distance D(m)
Narrow Beam	10＜α≤18 18＜α≤29 29＜α≤46	D≥75 75＞D≥65 65＞D≥55
Middle Beam	46＜α≤70 70＜α≤100	55＞D≥45 45＞D≥35
Wide Beam	100＜α≤130 α＞130	35＞D≥25 D＜25

Note: The beam angle in this table is based on the included angle of 10% of the maximum light intensity.

3. Application of beam angle

Sports lighting often uses an angle of 10% maximum light intensity, while lighting in other places generally uses an angle of 50% maximum light intensity.

Figure 2 Application of Sports Lighting

Narrow light distribution lamps are often used for projecting distant lighting, such as the lighting of large sports venues, high-rise buildings, columns and suspension cables of suspension bridges, etc. It should be noted that the 3 ° angle projection light in landscape lighting may exceed 10 ° angle according to sports lighting. These are two description methods that cause the same light to have different beam angle values, which can easily cause confusion in engineering. When designing and ordering, it is important to carefully indicate!

Application of Figure 3 in Landscape Lighting